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Step : The SWI/SNF complex acts to decondense the chromatin, thereby exposing histone tails. Step : A GCN5 containing histone acetylase complex associates with bound SWI5 and acetylates histone tails in the *HO* locus as SWI/SNF continues to decondense adjacent chromatin. Step : SWI5 is released from the DNA, but the S... | {
"Header 1": "TRANSCRIPTIONAL CONTROL OF GENE EXPRESSION",
"Header 2": "Structurally Diverse Activation and Repression Domains Regulate Transcription",
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The subsequent deacetylation of histone N-terminal tails in nucleosomes near the repressor-binding site inhibits interaction between the promoter DNA and general transcription factors, thereby repressing transcription initiation (see Figure 11-32a).
- Some activation domains function by binding multiprotein co-activato... | {
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"Header 2": "Structurally Diverse Activation and Repression Domains Regulate Transcription",
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In the absence of their hormone ligand, they repress transcription when bound to their cognate sites in DNA. They do so by directing histone deacetylation at nearby nucleosomes by the mechanism described earlier (see Figure 11-32a). As we saw earlier, in the presence of hormone, the ligand-binding domain of the RAR mon... | {
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"Header 2": "Structurally Diverse Activation and Repression Domains Regulate Transcription",
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In eukaryotes, the mechanisms for terminating transcription differ for each of the three RNA polymerases. Transcription of pre-rRNA genes by RNA polymerase I is terminated by a mechanism that requires a polymerase-specific termination factor. This DNA-binding protein binds to a specific DNA sequence downstream of the t... | {
"Header 1": "TRANSCRIPTIONAL CONTROL OF GENE EXPRESSION",
"Header 2": "11.7 Regulated Elongation and Termination of Transcription",
"token_count": 492,
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Currently, transcription of the human immunodeficiency virus (HIV) genome by RNA polymerase II provides the best-understood example of regulated transcription termination in eukaryotes. Efficient expression of HIV genes requires a small viral protein encoded at the *tat* locus. Cells infected
with $tat^-$ mutants p... | {
"Header 1": "TRANSCRIPTIONAL CONTROL OF GENE EXPRESSION",
"Header 2": "Transcription of the HIV Genome Is Regulated by an Antitermination Mechanism",
"token_count": 2001,
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157–172.]
Assembly of a fully active Pol I initiation complex begins with binding of a multimeric upstream activating factor (UAF) to the upstream element (Figure 11-46). Two of the six subunits composing UAF are histones, which probably participate in DNA binding. Next, a trimeric core factor binds to the core eleme... | {
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"Header 2": "Transcription of the HIV Genome Is Regulated by an Antitermination Mechanism",
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How are the vast differences in the frequency of transcription initiation at various genes achieved? What happens to the multiple interactions between activation domains, co-activator complexes, general transcription factors, and RNA polymerase II when the polymerase initiates transcription and transcribes away from th... | {
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"Header 2": "Transcription of the HIV Genome Is Regulated by an Antitermination Mechanism",
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2000. *Arabidopsis* transcription factors: genome-wide comparative analysis among eukaryotes. *Science* **290**:2105–2110.
Tupler, R., G. Perini, and M. R. Green. 2001. Expressing the human genome. *Nature* **409**:832–833.
#### Transcription Initiation by RNA Polymerase II
Woychik, N. A., and M. Hampsey. 2002. T... | {
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"Header 2": "Transcription of the HIV Genome Is Regulated by an Antitermination Mechanism",
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Portion of a "lampbrush chromosome" from an oocyte of the newt *Nophthalmus viridescens*; hnRNP protein associated with nascent RNA transcripts fluoresces red after staining with a monoclonal antibody. [Courtesy of M. Roth and J. Gall.]
n the previous chapter, we saw that most genes ar... | {
"Header 1": "12",
"Header 2": "POST-TRANSCRIPTIONAL GENE CONTROL AND NUCLEAR TRANSPORT",
"token_count": 406,
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After nascent RNA molecules produced by RNA polymerase II reach a length of 25–30 nucleotides, 7-methylguanosine and the other components of the $5^{\prime}$ cap found on eukaryotic
#### OUTLINE
- 12.1 Processing of Eukaryotic Pre-mRNA
- 12.2 Regulation of Pre-mRNA Processing
- 12.3 Macromolecular Transport Acros... | {
"Header 1": "12",
"Header 2": "The 5' Cap Is Added to Nascent RNAs Shortly After Initiation by RNA Polymerase II",
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Nascent RNA transcripts from protein-coding genes and mRNA processing intermediates, collectively referred to as **pre-mRNA**, do not exist as free RNA molecules in the nuclei of eukaryotic cells. From the time nascent transcripts first emerge from RNA polymerase II until mature mRNAs are transported into the cytoplasm... | {
"Header 1": "12",
"Header 2": "Pre-mRNAs Are Associated with hnRNP Proteins Containing Conserved RNA-Binding Domains",
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In eukaryotic cells, all mRNAs, except histone mRNAs, have a 3' poly(A) tail. Early studies of pulse-labeled adenovirus and SV40 RNA demonstrated that the viral primary transcripts extend beyond the site in the viral mRNAs from which the poly(A) tail extends. These results suggested that A residues are added to a 3' hy... | {
"Header 1": "12",
"Header 2": "3' Cleavage and Polyadenylation of Pre-mRNAs Are Tightly Coupled",
"token_count": 1992,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
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Such analysis of a large number of different mRNAs revealed moderately conserved, short consensus sequences at the splice sites flanking introns in eukaryotic pre-mRNAs; in higher organisms, a pyrimidine-rich region just upstream of the 3' splice site also is common (Figure 12-6). Studies with deletion mutants have sho... | {
"Header 1": "12",
"Header 2": "3' Cleavage and Polyadenylation of Pre-mRNAs Are Tightly Coupled",
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Five U-rich **small nuclear RNAs** (**snRNAs**), designated U1, U2, U4, U5, and U6, participate in pre-mRNA splicing. Ranging in length from 107 to 210 nucleotides, these snRNAs are associated with 6 to 10 proteins in *small nuclear ribonucleoprotein particles* (*snRNPs*) in the nucleus of eukaryotic cells.
Definitiv... | {
"Header 1": "12",
"Header 2": "snRNAs Base-Pair with Pre-mRNA and with One Another During Splicing",
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"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
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According to the current model of pre-mRNA splicing, the five splicing snRNPs are thought to assemble on the pre-mRNA, forming a large ribonucleoprotein complex called a **spliceosome** (Figure 12-9). Assembly of a spliceosome begins with the base pairing of the snRNAs of the U1 and U2
snRNPs to the pre-mRNA (see Fig... | {
"Header 1": "12",
"Header 2": "Spliceosomes, Assembled from snRNPs and a Pre-mRNA, Carry Out Splicing",
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The truncated mRNA produced in this case is either degraded or translated into a mutant, abnormally functioning protein. Recent studies have implicated this type of mutation in human genetic diseases. For example, *spinal muscle atrophy* is one of the most common genetic causes of childhood mortality. This disease resu... | {
"Header 1": "12",
"Header 2": "Spliceosomes, Assembled from snRNPs and a Pre-mRNA, Carry Out Splicing",
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Under certain nonphysiological in vitro conditions, pure preparations of some RNA transcripts slowly splice out introns in the absence of any protein. This observation led to recognition that some introns are *self-splicing*. Two types of self-splicing introns have been discovered: *group I introns*, present in nuclear... | {
"Header 1": "12",
"Header 2": "Self-Splicing Group II Introns Provide Clues to the Evolution of snRNAs",
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"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
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In addition the exosome appears to degrade pre-mRNAs that have not been properly spliced or polyadenylated. It is not yet clear how the exosome recognizes improperly processed pre-mRNAs.
To avoid being degraded by nuclear exonucleases, nascent transcripts, pre-mRNA processing intermediates, and mature mRNAs in the nu... | {
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"Header 2": "Self-Splicing Group II Introns Provide Clues to the Evolution of snRNAs",
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In female embryos, however, binding of Sxl protein to the 3 end of the intron between exons 1 and 2 blocks binding of U2AF at this site. The interaction of Sxl with *transformer* pre-mRNA is mediated by two RRM domains in the protein (see Figure 12-3). When Sxl is bound, U2AF binds to a lower-affinity site farther 3 in... | {
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"Header 2": "Self-Splicing Group II Introns Provide Clues to the Evolution of snRNAs",
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As is evident from Figure 12-14, the *Drosophila* Sxl protein and Tra protein have opposite effects: Sxl prevents splicing, causing exons to be skipped, whereas Tra promotes splicing. The action of similar proteins may explain the cell-typespecific expression of fibronectin isoforms in humans. For instance, an Sxl-like... | {
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"Header 2": "Splicing Repressors and Activators Control Splicing at Alternative Sites",
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This mRNA is translated into apoB-100, which has two functional domains: an N-terminal domain (green) that associates with lipids and a C-terminal domain (orange) that binds to LDL receptors on cell membranes.
In the *apo-B* mRNA produced in the intestine, the CAA codon in exon 26 is edited to a UAA stop codon. As a ... | {
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A current model for the import of cytoplasmic cargo proteins mediated by a monomeric importin is shown in Figure 12-21. Free importin in the cytoplasm binds to its cognate NLS in a cargo protein, forming a *bimolecular cargo complex.* The cargo complex then translocates through the NPC channel as the importin binds t... | {
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(a) A fixed preparation viewed by phasecontrast microscopy includes unfused HeLa cells (arrowhead) and *Xenopus* cells (dotted arrow), as well as fused heterokaryons
(solid arrow). In the heterokaryon in this micrograph, the round HeLa-cell nucleus is to the right of the oval-shaped *Xenopus* nucleus. (b, c) When the... | {
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The finding that the mRNA-exporter is associated with mRNPs and binds directly to FG repeats led to the model of mRNP transport depicted in Figure 12-24. This model proposes that the mRNA-exporter translocates mRNPs through the nuclear pore channel similarly to the karyopherins, that is, by binding transiently to succe... | {
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Here we describe the regulation
- **FIGURE 12-25 Formation of heterogeneous ribonucleoprotein particles (hnRNPs) and export of mRNPs from the nucleus.** (a) Model of a single chromatin transcription loop and assembly of Balbiani ring (BR) mRNP in *Chironomous tentans*. Nascent RNA tran... | {
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In this section we consider other mechanisms of posttranscriptional control that contribute to regulating the expression of some genes. Most of these mechanisms operate in the cytoplasm, controlling the stability or localization of mRNA or its translation into protein. We begin by discussing two recently discovered a... | {
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A different mechanism involving RNA-binding proteins that interact with 5 regulatory elements is discussed later.
Sequence-specific translation-control proteins may bind cooperatively to neighboring sites in 3 UTRs and function in a combinatorial manner, similar to the cooperative binding of transcription factors to ... | {
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Many short-lived mRNAs in mammalian cells contain multiple, sometimes overlapping, copies of the sequence AUUUA in their 3 untranslated region. Specific RNA-binding
▲ **FIGURE 12-29 Pathways for degradation of eukaryotic mRNAs.** In the deadenylation-dependent (*middle*) pathways, th... | {
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In later chapters we examine how some proteins are transported *after* their synthesis to their proper cellular location. Alternatively, protein localization might be achieved by localization of mRNAs to specific regions of the cell cytoplasm in which their encoded proteins function. In most cases examined thus far, su... | {
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Pre-rRNA transcription units are arranged in tandem, separated by nontranscribed spacer regions of nucleolar chromatin. [Courtesy of Y. Osheim and O. J. Miller, Jr.]
mans (Figure 12-32). Second, the genomic regions corresponding to the three mature rRNAs are always arranged in the same 5→3 order: 18S, 5.8S, and 28S. ... | {
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The DNA in the protozoan *Tetrahymena thermophila* contains an intervening intron in the region that encodes the large pre-rRNA molecule. Careful searches failed to uncover even one pre-rRNA gene without the extra sequence, indicating that splicing is required to produce mature rRNA in these organisms. In vitro studies... | {
"Header 1": "12",
"Header 2": "Self-Splicing Group I Introns Were the First Examples of Catalytic RNA",
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Mature cytosolic tRNAs, which average 75–80 nucleotides in length, are produced from larger precursors (pre-tRNAs) synthesized by RNA polymerase III in the nucleoplasm. Mature tRNAs also contain numerous modified bases that are not present in tRNA primary transcripts. Cleavage and base modification occur during process... | {
"Header 1": "12",
"Header 2": "Pre-tRNAs Undergo Cleavage, Base Modification, and Sometimes Protein-Catalyzed Splicing",
"token_count": 1988,
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#### **KEY TERMS**
5 cap *493* alternative splicing *505* cargo complex *510* cleavage/polyadenylation complex *497* cross-exon recognition complex *501* exosome *504* exportin 1 *512* FG-nucleoporins *510* group I introns *502* group II introns *502* importins *510* iron-response element–binding protein (IRE-BP) *... | {
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"Header 2": "Pre-tRNAs Undergo Cleavage, Base Modification, and Sometimes Protein-Catalyzed Splicing",
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A conserved mRNA export machinery coupled to pre-mRNA splicing. *Cell* **108**:523–531.
Ribbeck, K., and D. Gorlich. 2001. Kinetic analysis of translocation through nuclear pore complexes. *Embo. J.* **20**:1320–1330.
Rout, M. P., and J. D. Aitchison. 2001. The nuclear pore complex as a transport machine. *J. Biol.... | {
"Header 1": "12",
"Header 2": "Pre-tRNAs Undergo Cleavage, Base Modification, and Sometimes Protein-Catalyzed Splicing",
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Three-dimensional structure of the G protein $\beta$ (blue) and $\gamma$ (purple) complex as obtained by x-ray crystallography.
o cell lives in isolation. In eukaryotic microorganisms such as yeast, slime molds, and protozoans, secreted molecules called **pheromones** coordinate th... | {
"Header 1": "12",
"Header 2": "SIGNALING AT THE CELL SURFACE",
"token_count": 2047,
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In general, the first type of response occurs more rapidly than the second type. Signaling from G protein–coupled receptors, described in later sections, often results in changes in the activity of preexisting proteins, although activation of these receptors on some cells also can induce changes in gene expression.
T... | {
"Header 1": "12",
"Header 2": "SIGNALING AT THE CELL SURFACE",
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As we've seen, activation of a cell-surface receptor and subsequent signal transduction are triggered by binding of a signaling molecule (ligand) to the receptor. This binding depends on weak, noncovalent forces (i.e., ionic, van der Waals, and hydrophobic interactions) and **molecular complementarity** between the int... | {
"Header 1": "12",
"Header 2": "Maximal Cellular Response to a Signaling Molecule May Not Require Activation of All Receptors",
"token_count": 1992,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
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Cell-surface receptors are difficult to identify and purify, mainly because they are present in such minute amounts. The receptor for a particular signaling molecule commonly constitutes only $\approx 10^{-6}$ of the total protein in the cell, or $\approx 10^{-4}$ of the plasma-membrane protein. Purification is als... | {
"Header 1": "12",
"Header 2": "Binding Assays Are Used to Detect Receptors and Determine Their $K_d$ Values",
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A *functional expression assay* of the cloned cDNA in a mammalian cell that normally lacks the encoded receptor can provide definitive proof that the proper protein indeed has been obtained (Figure 13-6). Such expression assays also permit investigators to study the effects of mutating specific amino acids on ligand bi... | {
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"Header 2": "Binding Assays Are Used to Detect Receptors and Determine Their $K_d$ Values",
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The rate of GTP hydrolysis frequently is enhanced by a *GTPase-accelerating protein (GAP),* whose activity also may be controlled by extracellular signals. The rate of GTP hydrolysis regulates the length of time the switch protein remains in the active conformation and able to signal downstream.
There are two classes... | {
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"Header 2": "Binding Assays Are Used to Detect Receptors and Determine Their $K_d$ Values",
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Cell Sci.* 114:3219; part (b) adapted from C. Garner, J. Nash, and R. Huganir, 2000, *Trends Cell Biol.* 10:274.]
#### Appropriate Cellular Responses Depend on Interaction and Regulation of Signaling Pathways
In this chapter and the next, we focus primarily on simple signal-transduction pathways triggered by ligand... | {
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"Header 2": "Binding Assays Are Used to Detect Receptors and Determine Their $K_d$ Values",
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■ The level of second messengers, such as Ca<sup>2+</sup>, cAMP, and IP<sub>3</sub>, increases or occasionally decreases in response to binding of ligand to cell-surface receptors (see Figure 13-7). These nonprotein intracellular signaling molecules,
in turn, regulate the activities of enzymes and nonenzymatic protei... | {
"Header 1": "12",
"Header 2": "**KEY CONCEPTS OF SECTION 13.2** Intracellular Signal Transduction",
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We now turn our attention to the very large group of cellsurface receptors that are coupled to signal-transducing trimeric G proteins. All G protein-coupled receptors (GPCRs) contain seven membrane-spanning regions with their N-terminal segment on the exoplasmic face and their C-terminal segment on the cytosolic face o... | {
"Header 1": "12",
"Header 2": "13.3 G Protein–Coupled Receptors That Activate or Inhibit Adenylyl Cyclase",
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Figure 13-11 illustrates how G protein–coupled receptors transduce signals from extracellular hormones to associated effector proteins. Both the $G_{\alpha}$ and $G_{\gamma}$ subunits are linked to the membrane by covalently attached lipids. In the resting state, when no ligand is bound to the receptor, the $G_{\a... | {
"Header 1": "12",
"Header 2": "The $G_{\\alpha}$ Subunit of G Proteins Cycles Between Active and Inactive Forms",
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acteristic of YFP. However, if ligand binding leads to dissociation of the $G_{\alpha}$ and $G_{\beta\gamma}$ subunits, then fluorescence energy transfer cannot occur. In this case, irradiation of cells at 440 nm causes emission of 490-nm light (cyan) characteristic of CFP (*right*). (b) Plot of the emission of yel... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
Epinephrine is particularly important in mediating the body's response to stress, such as fright or heavy exercise, when all tissues have an increased need to catabolize glucose and fatty acids to produce ATP. These principal metabolic fuels can be supplied to the blood in seconds by the rapid breakdown of glycogen to ... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
(b) Three-dimensional structure of $G_{s\alpha}$ -GTP complexed with two fragments encompassing the catalytic domain of adenylyl cyclase determined by x-ray crystallography. The α3-β5 loop and the helix in the switch II region (blue) of $G_{s\alpha}$ GTP interact simultaneously with a specific region of adenylyl cyc... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
The versatile trimeric G proteins enable different receptor-hormone complexes to modulate the activity of the same effector protein. In the liver, for instance, glucagon and epinephrine bind to different receptors, but both receptors interact with and activate the same $G_{\rm s},$ which activates adenylyl cyclase, t... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
In multicellular animals virtually all the diverse effects of cAMP are mediated through protein kinase A (PKA), also called cAMP-dependent protein kinase. As discussed in Chapter 3, inactive PKA is a tetramer consisting of two regulatory (R) subunits and two catalytic (C) subunits. Each R subunit has two distinct cAMP-... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
For example, blood levels of epinephrine as low as $10^{-10}$ M can stimulate liver glycogenolysis and release of glucose. An epinephrine stimulus of this magnitude generates an intracellular cAMP concentration of $10^{-6}$ M, an amplification of $10^4$ . Because three more catalytic steps precede the release of g... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
Several factors contribute to termination of the response to hormones recognized by $\beta$ -adrenergic receptors and other receptors coupled to $G_s$ . First, the affinity of the receptor for hormone decreases when the GDP bound to $G_{s\alpha}$ is replaced with a GTP following hormone binding. This increase in th... | {
"Header 1": "**EXPERIMENTAL FIGURE 13-12 Receptor-mediated** activation of coupled G proteins occurs within a few seconds of ligand binding in living cells. The amoeba *Dictyostelium discoideum* was transfected with genes encoding two fusion proteins: a $G_{\\alpha}$ fused to cyan fluorescent protein (CFP), a mutan... |
additional function of β-arrestin in regulating cell-surface receptors initially was suggested by the observation that loss of cell surface β-adrenergic receptors in response to ligand binding is stimulated by overexpression of BARK and βarrestin. Subsequent studies revealed that β-arrestin binds not only to phosphoryl... | {
"Header 1": "**A FIGURE 13-19** Role of β-arrestin in GPCR desensitization and signal transduction. β-Arrestin binds to phosphorylated serine and tyrosine residues in the C-terminal segment of G protein–coupled receptors (GPCRs). Clathrin and AP2, two other proteins bound by β-arrestin, promote endocytosis of the r... |
In many cell types, a rise in the cAMP level may produce a response that is required in one part of the cell but is unwanted, perhaps deleterious, in another part. A family of anchoring proteins localizes PKA isoforms to specific subcellular locations, thereby restricting cAMP-dependent responses to these locations. Th... | {
"Header 1": "**A FIGURE 13-19** Role of β-arrestin in GPCR desensitization and signal transduction. β-Arrestin binds to phosphorylated serine and tyrosine residues in the C-terminal segment of G protein–coupled receptors (GPCRs). Clathrin and AP2, two other proteins bound by β-arrestin, promote endocytosis of the r... |
excess of that which can be degraded by PDE. The resulting binding of cAMP to the regulatory (R) subunits of PKA releases the active catalytic (C) subunits. Step : Subsequent phosphorylation of PDE by PKA stimulates its catalytic activity, thereby driving cAMP levels back to basal and causing reformation of the inactiv... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
- Trimeric G proteins transduce signals from coupled cellsurface receptors to associated effector proteins, which are either enzymes that form second messengers or cation channel proteins (see Table 13-1).
- Signals most commonly are transduced by $G_{\alpha}$ , a GTPase switch protein that alternates between an activ... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
As we learned in Chapter 7, many neurotransmitter receptors are ligand-gated ion channels. These include some types of glutamate and serotonin receptors, as well as the nicotinic acetylcholine receptor found at nerve-muscle synapses. Many
neurotransmitter receptors, however, are G protein–coupled receptors. The effec... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
These receptors are linked via a trimeric G protein to K<sup>+</sup> channels. Binding of acetylcholine triggers activation of the $G_{i\alpha}$ subunit and its dissociation from the $G_{\beta\gamma}$ subunit in the usual way (see Figure 13-11). In this case, the released $G_{\beta\gamma}$ subunit (rather than $... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
The key transducing molecule linking activated opsin to the closing of cation channels in the rod-cell plasma membrane is the second messenger **cyclic GMP (cGMP)**. Rod outer segments contain an unusually high concentration (≈0.07 mM) of cGMP, which is continuously formed from GTP in a reaction catalyzed by guanylyl c... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
Cone cells are insensitive to low levels of illumination, and the activity of rod cells is inhibited at high light levels. Thus when we move from daylight into a dimly lighted room, we are initially blinded. As the rod cells slowly become sensitive to the dim light, we gradually are able to see and distinguish objects.... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
- The cardiac muscarinic acetylcholine receptor is a GPCR whose effector protein is a $K^+$ channel. Receptor activation causes release of the $G_{\beta\gamma}$ subunit, which opens $K^+$ channels (see Figure 13-21). The resulting hyperpolarization of the cell membrane slows the rate of heart muscle contraction.
... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
In this section, we discuss GPCR-triggered signal-transduction pathways involving several other second messengers and the mechanisms by which they regulate various cellular activities. A number of these second messengers are derived from *phosphatidylinositol (PI)*. The inositol group in this phospholipid, which extend... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
Most intracellular $Ca^{2+}$ ions are sequestered in the mitochondria and in the lumen of the endoplasmic reticulum (ER) and other vesicles. Cells employ various mechanisms for regulating the concentration of $Ca^{2+}$ ions in the cytosol, which usually is kept below $0.2~\mu\mathrm{M}$ . For instance, $Ca^{2+}$ ... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
This pathway can be triggered by ligand binding to certain G protein-coupled receptors and several other receptor types, leading to activation of phospholipase C. Cleavage of PIP2 by phospholipase C yields IP3 and DAG (step 11). After diffusing through the cytosol, IP3 interacts with and opens Ca<sup>2+</sup> channels ... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
The cell-surface receptor for atrial natriuretic factor (ANF) also has intrinsic guanylyl cyclase activity (not shown); stimulation of this receptor on smooth muscle cells also leads to increased cGMP and subsequent muscle relaxation. PP<sub>i</sub> = pyrophosphate. [See C. S. Lowenstein et al., 1994, Ann. Intern. Med.... | {
"Header 1": "A FIGURE 13-20 Localization of protein kinase A (PKA) to the nuclear membrane in heart muscle. This A kinase–associated protein mAKAP anchors both PKA and cAMP phosphodiesterase (PDE) to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the cAMP lev... |
#### **CREB Links cAMP Signals to Transcription**
In mammalian cells, an elevation in the cytosolic cAMP level stimulates the expression of many genes. For instance, increased cAMP in certain endocrine cells induces production of somatostatin, a peptide that inhibits release of various... | {
"Header 1": "▶ FIGURE 13-32 Activation of gene expression following ligand binding to G<sub>s</sub> protein-coupled receptors. Receptor stimulation (■) leads to activation of PKA (②). Catalytic subunits of PKA translocate to the nucleus (③) and there phosphorylate and activate the transcription factor CREB (④). Pho... |
For which receptor does the ligand show the greater affinity? Calculate the fraction of receptors that have a bound ligand ([RL]/RT) for ligand with receptor 1 and for ligand with receptor 2, if the concentration of free ligand is 10<sup>8</sup> M.
- **3.** A study of the properties of cell-surface receptors can be gre... | {
"Header 1": "▶ FIGURE 13-32 Activation of gene expression following ligand binding to G<sub>s</sub> protein-coupled receptors. Receptor stimulation (■) leads to activation of PKA (②). Catalytic subunits of PKA translocate to the nucleus (③) and there phosphorylate and activate the transcription factor CREB (④). Pho... |
*Trends Cell Biol.* **10**:274–280.
Harris, B. Z., and W. A. Lim. 2001. Mechanism and role of PDZ domains in signaling complex assembly. *J. Cell Sci.* **114**:3219–3231.
Rebecchi, M. J., and S. Scarlata. 1998. Pleckstrin homology domains: a common fold with diverse functions. *Ann. Rev. Biophys. Biomol. Struc.* **... | {
"Header 1": "▶ FIGURE 13-32 Activation of gene expression following ligand binding to G<sub>s</sub> protein-coupled receptors. Receptor stimulation (■) leads to activation of PKA (②). Catalytic subunits of PKA translocate to the nucleus (③) and there phosphorylate and activate the transcription factor CREB (④). Pho... |
Fluorescence resonance energy transfer (FRET) detects time and location of activation of Ras protein in live cells triggered by epidermal growth factor. [Michiyuki Matsuda, Research Institute for Microbial Diseases, Osaka University.]
he development of all organisms requires execution o... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"token_count": 546,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
In the case of receptor
#### OUTLINE
- 14.1 TGF $\beta$ Receptors and the Direct Activation of Smads
- 14.2 Cytokine Receptors and the JAK-STAT Pathway
- 14.3 Receptor Tyrosine Kinases and Activation of Ras
- 14.4 MAP Kinase Pathways
- 14.5 Phosphoinositides as Signal Transducers
- 14.6 Pathways That Involve Signa... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"token_count": 2030,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
For simplicity, we often describe the various receptor classes independently, concentrating on the major pathway of **signal transduction** initiated by each class of receptor. However, as shown in Table 14-1, several classes of receptors can transduce signals by more than one pathway. Moreover, many genes are regula... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"token_count": 339,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
A number of related extracellular signaling molecules that play widespread roles in regulating development in both invertebrates and vertebrates constitute the *transforming*
growth factor $\beta$ (TGF $\beta$ ) superfamily. One member of this superfamily, bone morphogenetic protein (BMP), initially was identified ... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "14.1 TGFβ Receptors and the Direct Activation of Smads",
"token_count": 426,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
In humans TGFβ consists of three protein isoforms, TGFβ-1, TGFβ-2, and TGFβ-3, each encoded by a unique gene and expressed in both a tissue-specific and developmentally regulated fashion. Each TGFB isoform is synthesized as part of a larger precursor that contains a pro-domain. This domain is cleaved from but remains n... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "TGF $\\beta$ Is Formed by Cleavage of a Secreted Inactive Precursor",
"token_count": 700,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
To identify the cell-surface TGF $\beta$ receptors, investigators first reacted the purified growth factor with the radioisotope iodine-125 (\$^{125}I) under conditions such that the radioisotope covalently binds to exposed tyrosine residues. The \$^{125}I-labeled TGF $\beta$ protein was incubated with cultured cells... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "TGF $\\beta$ Signaling Receptors Have Serine/Threonine Kinase Activity",
"token_count": 351,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Researchers identified the transcription factors downstream from TGF $\beta$ receptors in *Drosophila* from genetic studies similar to those used to dissect receptor tyrosine kinase pathways (see Section 14.3). These transcription factors in *Drosophila* and the related vertebrate proteins are now called **Smads**. Th... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Activated Type I TGF $\\beta$ Receptors Phosphorylate Smad Transcription Factors",
"token_count": 1604,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Smad signaling is regulated by additional intracellular proteins, including two cytosolic proteins called *SnoN* and *Ski* (Ski stands for "Sloan-Kettering Cancer Institute"). These proteins were originally identified as **oncoproteins** because they cause abnormal cell proliferation when overexpressed in cultured fibr... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Oncoproteins and I-Smads Regulate Smad Signaling via Negative Feedback Loops",
"token_count": 591,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Many human tumors contain inactivating mutations in either $TGF\beta$ receptors or Smad proteins, and thus are resistant to growth inhibition by
TGF $\beta$ (see Figure 23-20). Most human pancreatic cancers, for instance, contain a deletion in the gene encoding Smad4 and thus canno... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Loss of TGF**β** Signaling Contributes to Abnormal Cell Proliferation and Malignancy",
"token_count": 2017,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Socolovsky et al., 2001, *Blood* **98**:3261.]
bind IRS1 or other multidocking proteins via a PTB domain in the docking protein (Figure 14-6).The activated receptor then phosphorylates the bound docking protein, forming many phosphotyrosines that in turn serve as docking sites for SH2-containing signaling proteins. S... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Loss of TGF**β** Signaling Contributes to Abnormal Cell Proliferation and Malignancy",
"token_count": 1543,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Soon after the discovery and cloning of cytokines, most of their receptors were isolated by expression cloning or other strategies. Elucidation of the essential components of their intracellular signaling pathways, however, awaited development of new types of genetic approaches using cultured mammalian cells. In these ... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 2037,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
A phosphorylated STAT dissociates spontaneously from the receptor, and two phosphorylated STAT proteins form a dimer in which the SH2 domain on each binds to the phosphotyrosine in the other. Because dimerization exposes the nuclear-localization signal (NLS), STAT dimers move into the nucleus, where they bind to specif... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 2028,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
#### **Mutant Erythropoietin Receptor That Cannot Be Down-Regulated Leads to Increased Hematocrit**
In normal adult men and women, the percentage of erythrocytes in the blood (the *hematocrit*) is maintained very close to 45– 47 percent. A drop in the hematocrit results in increased production of erythropoietin by ... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 1949,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
▲ **FIGURE 14-15 Structure of the dimerized ligand-bound receptor for fibroblast growth factor (FGF), which is stabilized by heparan sulfate.** Shown here are side and top views of the complex comprising the extracellular domains of two FGF receptor (FGFR)... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 2024,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
In mutant flies that do not express a functional Boss protein or Sev RTK, interaction between the Boss and Sev proteins cannot occur, and no R7 cells develop (Figure 14-18b).
To identify intracellular signal-transducing proteins in the Sev RTK pathway, investigators produced mutant flies expressing a temperature-sens... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 2005,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
The resulting conformational change in Switch I and Switch II segments of Ras, allowing both to bind to the GTP phosphate (see Figure 13-8), displaces Sos and promotes interaction of RasGTP with its effectors (discussed later). [Adapted from P. A. Boriack-Sjodin and J. Kuriyan, 1998, *Nature* **394**:341.]
relocaliza... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"token_count": 1011,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
A remarkable convergence of biochemical and genetic studies in yeast, *C. elegans, Drosophila,* and mammals has revealed a highly conserved cascade of protein kinases that operates
Hormone Res. 56:127; and M. Yip-Schneider et al., 2000, Biochem. J. 351:151.]
in sequential fashion downstream from activated Ras (Figu... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"Header 3": "Signals Pass from Activated Ras to a Cascade of Protein Kinases",
"token_count": 1950,
"source_pdf": "datasets/websources/biochem/s... |
As depicted in Figure 14-23, activated (phosphorylated) dimeric MAP kinase induces transcription of the *c-fos* gene by modifying two transcription factors, *ternary complex factor (TCF)* and *serum response factor (SRF).* In the cytosol, MAP kinase phosphorylates and activates another kinase, p90RSK, which transloca... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Somatic Cell Genetics Revealed JAKs and STATs as Essential Signal-Transduction Proteins",
"Header 3": "Signals Pass from Activated Ras to a Cascade of Protein Kinases",
"token_count": 659,
"source_pdf": "datasets/websources/biochem/s-... |
Although many MAP kinase pathways are initiated by RTKs or cytokine receptors, signaling from other receptors can activate MAP kinase in different cell types of higher eukaryotes. Moreover, yeasts and other single-celled eukaryotes, which lack cytokine receptors or RTKs, do possess several MAP kinase pathways. To illus... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "G Protein–Coupled Receptors Transmit Signals to MAP Kinase in Yeast Mating Pathways",
"token_count": 637,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
The receptors for yeast **a** and $\alpha$ mating factors are coupled to the same trimeric G protein. Ligand binding leads to activation and dissociation of the G protein (see Figure 13-10). In the yeast mating pathway, the dissociated G<sub>By</sub> activates a protein kinase cascade analogous to the cascade downstr... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "► FIGURE 14-24 Kinase cascade that transmits signals downstream from mating factor receptors in *S. cerevisiae*.",
"token_count": 529,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
In addition to the MAP kinases discussed above, both yeasts and higher eukaryotic cells contain other members of the MAP kinase superfamily. These include mammalian *Jun N-terminal kinases (JNKs)* and *p38 kinases,* which become activated by various types of stresses, and six yeast kinases described below. Collectively... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Scaffold Proteins Isolate Multiple MAP Kinase Pathways in Eukaryotic Cells",
"token_count": 2020,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Chem.* **274**:8347.]
cruiting the enzyme phosphatidylinositol-3 kinase to the membrane. PI-3 kinase was first identified as a kinase that copurifies with several viral oncoproteins such as the "middle T" protein encoded by polyoma virus. When inactive, dominant negative, versions of PI-3 kinase are expressed in viru... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Scaffold Proteins Isolate Multiple MAP Kinase Pathways in Eukaryotic Cells",
"token_count": 2015,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
For example, genetic manipulation of the Ras–MAP kinase and PI-3 kinase pathways during muscle differentiation indicates that these pathways have opposite phenotypic effects: activation of the Ras–MAP kinase pathway inhibits myocyte differentiation into myotubes, whereas activation of the PI-3 kinase pathway promotes i... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Scaffold Proteins Isolate Multiple MAP Kinase Pathways in Eukaryotic Cells",
"token_count": 743,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Up to now we have discussed reversible signaling pathways, where inactivation is as important as the initial activation. In contrast are essentially irreversible pathways in which a component is proteolytically cleaved. Here we consider two such pathways: the *NF-κB pathway*, which enables cells to respond immediately ... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "14.6 Pathways That Involve Signal-Induced Protein Cleavage",
"token_count": 1472,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Both Notch and its ligand Delta are transmembrane proteins with numerous EGF-like repeats in their extracellular domains. They participate in a highly conserved and important type of cell differentiation in both invertebrates and vertebrates, called **lateral inhibition**, in which adjacent and developmentally equivale... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Regulated Intramembrane Proteolysis Catalyzed by Presenilin 1 Activates Notch Receptor",
"token_count": 2026,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Here we discuss two other mechanisms by which signaling pathways are down-regulated: removal of receptors from the cell surface by endocytosis, and secretion of proteins that bind and sequester hormones, thus preventing their interaction with cellsurface receptors.
#### **Endocytosis of Cell-Surface Receptors Desensi... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Regulated Intramembrane Proteolysis Catalyzed by Presenilin 1 Activates Notch Receptor",
"token_count": 843,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Another way of reducing the activity of cell-surface receptors is secretion of a protein that contains a hormone-binding segment but no signal-transducing activity. As might be expected, hormone binding to such proteins, called *decoy receptors*, reduces the amount of hormone available to bind to receptors capable of s... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Secreted Decoy Receptors Bind Hormone and Prevent Receptor Activation",
"token_count": 2034,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
The activity of several kinases, such as Raf and protein kinase B (PKB), is controlled by inhibitory domains as well as by multiple phosphorylations catalyzed by several other kinases. But our understanding of how the activity of these and other kinases is precisely regulated to meet the cell's needs will require addit... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Secreted Decoy Receptors Bind Hormone and Prevent Receptor Activation",
"token_count": 2040,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
Role of transforming growth factor beta in human disease. *N. Eng. J. Med.* **342**:1350–1358.
Liu, X., Y. Sun, R. Weinberg, and H. Lodish. 2001. Ski/Sno and TGF-beta signaling. *Cytokine Growth Factor Rev*. **12**:1–8.
Massagué, J. 2000. How cells read TGF-beta signals. *Nature Rev. Mol. Cell Biol.* **1**:169–178.... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Secreted Decoy Receptors Bind Hormone and Prevent Receptor Activation",
"token_count": 2058,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
#### Pathways That Involve Signal-Induced Protein Cleavage
Brown, M., J. Ye, R. Rawson, and J. Goldstein. 2000. Regulated intramembrane proteolysis: a control mechanism conserved from bacteria to humans. *Cell* **100**:391–398.
Esler, W., and M. Wolfe. 2001. A portrait of Alzheimer secretases—new features and fam... | {
"Header 1": "SIGNALING PATHWAYS THAT CONTROL GENE ACTIVITY",
"Header 2": "Secreted Decoy Receptors Bind Hormone and Prevent Receptor Activation",
"token_count": 693,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
nherent in the full genome contained in most cells is the potential to form vastly diverse cell types, which perform an enormous variety of tasks. Each individual cell, however, employs only part of an organism's complete genetic repertoire. An array of external hormonal, metabolic, developmental, and environmental sig... | {
"Header 1": "INTEGRATION OF SIGNALS AND GENE CONTROLS",
"token_count": 2027,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
For example, the *Pax6* gene is employed in eye development in enormously diverse organisms, such as clams, flies, and humans, and the tinman gene is necessary for heart development in flies and humans. As discussed in Section 15.4, the Hox gene cluster controls head-to-tail organization of the body in almost all anima... | {
"Header 1": "INTEGRATION OF SIGNALS AND GENE CONTROLS",
"token_count": 2026,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
In retrospect, it makes sense, because the time during which fibroblasts are exposed to serum in an intact organism is when there is a wound. The results show the usefulness of microarrays in revealing unexpected responses by cells.
The developmental time course of gene transcription has been assessed with DNA microa... | {
"Header 1": "INTEGRATION OF SIGNALS AND GENE CONTROLS",
"token_count": 1916,
"source_pdf": "datasets/websources/biochem/s-molecularcellbiology.pdf"
} |
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