Showing papers by "Cold Spring Harbor Laboratory published in 1993"
TL;DR: It is found that over expression of p21 inhibits the activity of each member of the cyclin/CDK family, and this results indicate that p21 may be a universal inhibitor of cyclin kinases.
Abstract: Deregulation of cell proliferation is a hallmark of neoplastic transformation. Alteration in growth control pathways must translate into changes in the cell-cycle regulatory machinery, but the mechanism by which this occurs is largely unknown. Compared with normal human fibroblasts, cells transformed with a variety of viral oncoproteins show striking changes in the subunit composition of the cyclin-dependent kinases (CDKs). In normal cells, CDKs exist predominantly in multiple quaternary complexes, each containing a CDK, cyclin, proliferating cell nuclear antigen and the p21 protein. However, in many transformed cells, proliferating cell nuclear antigen and p21 are lost from these multiprotein enzymes. Here we have investigated the significance of this phenomenon by molecular cloning of p21 and in vitro reconstitution of the quaternary cell-cycle kinase complexes. We find that p21 inhibits the activity of each member of the cyclin/CDK family. Furthermore, overexpression of p21 inhibits the proliferation of mammalian cells. Our results indicate that p21 may be a universal inhibitor of cyclin kinases.
3,442 citations
TL;DR: The analysis of the differences between two complex genomes holds promise for the discovery of infectious agents and probes useful for genetic studies, and may also be used for isolating probes linked to sites of genomic rearrangements.
Abstract: The analysis of the differences between two complex genomes holds promise for the discovery of infectious agents and probes useful for genetic studies. A system was developed in which subtractive and kinetic enrichment was used to purify restriction endonuclease fragments present in one population of DNA fragments but not in another. Application of this method to DNA populations of reduced complexity ("representations") resulted in the isolation of probes to viral genomes present as single copies in human DNA, and probes that detect polymorphisms between two individuals. In principle, this system, called representational difference analysis (RDA), may also be used for isolating probes linked to sites of genomic rearrangements, whether occurring spontaneously and resulting in genetic disorders or cancer, or programmed during differentiation and development.
1,428 citations
TL;DR: It is reported that a growth factor-inducible gene, 3CH134, encodes a dual specificity phosphatase that dephosphorylates and inactivates p42MAPK both in vitro and in vivo, and the name MKP-1 is proposed for this phosphat enzyme.
1,181 citations
TL;DR: The results indicate that the Grbl/hSos1 complex couples activated EGF receptor to Ras signalling, and a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction.
Abstract: Many of the actions of receptor tyrosine kinases are mediated by the protein Ras, including the activation of various downstream serine/threonine kinases and the stimulation of growth and differentiation. The human protein Grb2 binds to ligand-activated growth factor receptors and downstream effector proteins through its Src-homology (SH) domains SH2 and SH3, respectively, and like its homologue from Caenorhabditis elegans, Sem-5, apparently forms part of a highly conserved pathway by which these receptors can control Ras activity. Here we show that the SH3 domains of Grb2 bind to the carboxy-terminal part of hSos1, the human homologue of the Drosophila guanine-nucleotide-releasing factor for Ras, which is essential for control of Ras activity by epidermal growth factor receptor and sevenless. Moreover, a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction. These results indicate that the Grb2/hSos1 complex couples activated EGF receptor to Ras signalling.
944 citations
TL;DR: The results suggest that the coupling of receptor tyrosine kinases to Ras signaling is mediated by a molecular complex consisting of GRB2 and hSos1, a guanine nucleotide exchange factor for Ras.
Abstract: A human complementary DNA was isolated that encodes a widely expressed protein, hSos1, that is closely related to Sos, the product of the Drosophila son of sevenless gene. The hSos1 protein contains a region of significant sequence similarity to CDC25, a guanine nucleotide exchange factor for Ras from yeast. A fragment of hSos1 encoding the CDC25-related domain complemented loss of CDC25 function in yeast. This hSos1 domain specifically stimulated guanine nucleotide exchange on mammalian Ras proteins in vitro. Mammalian cells overexpressing full-length hSos1 had increased guanine nucleotide exchange activity. Thus hSos1 is a guanine nucleotide exchange factor for Ras. The hSos1 interacted with growth factor receptor-bound protein 2 (GRB2) in vivo and in vitro. This interaction was mediated by the carboxyl-terminal domain of hSos1 and the Src homology 3 (SH3) domains of GRB2. These results suggest that the coupling of receptor tyrosine kinases to Ras signaling is mediated by a molecular complex consisting of GRB2 and hSos1.
762 citations
TL;DR: Two unrelated receptors may activate a common nuclear signal transduction pathway that, through differential use of latent cytoplasmic proteins, permits these receptors to regulate both common and unique sets of genes.
Abstract: Growth factors and cytokines act through cell surface receptors with different biochemical properties Yet each type of receptor can elicit similar as well as distinct biological responses in target cells, suggesting that distinct classes of receptors activate common gene sets Epidermal growth factor, interferon-gamma, and interleukin-6 all activated, through direct tyrosine phosphorylation, latent cytoplasmic transcription factors that recognized similar DNA elements However, different ligands activated different patterns of factors with distinct DNA-binding specificities in the same and different cells Thus, unrelated receptors may activate a common nuclear signal transduction pathway that, through differential use of latent cytoplasmic proteins, permits these receptors to regulate both common and unique sets of genes
683 citations
TL;DR: The ddm1 mutations were used to demonstrate that de novo DNA methylation in vivo is slow, and are associated with a segregation distortion phenotype.
Abstract: Three DNA hypomethylation mutants of the flowering plant Arabidopsis thaliana were isolated by screening mutagenized populations for plants containing centromeric repetitive DNA arrays susceptible to digestion by a restriction endonuclease that was sensitive to methylated cytosines. The mutations are recessive, and at least two are alleles of a single locus, designated DDM1 (for decrease in DNA methylation). Amounts of 5-methylcytosine were reduced over 70 percent in ddm1 mutants. Despite this reduction in DNA methylation levels, ddm1 mutants developed normally and exhibited no striking morphological phenotypes. However, the ddm1 mutations are associated with a segregation distortion phenotype. The ddm1 mutations were used to demonstrate that de novo DNA methylation in vivo is slow.
681 citations
TL;DR: Analysis of sequence motifs found in metazoan protein factors involved in constitutive pre-mRNA splicing and in alternative splicing regulation indicates that the RRM is an ancient conserved region (ACR) that has diversified by duplication of genes and intragenic domains.
Abstract: We present a systematic analysis of sequence motifs found in metazoan protein factors involved in constitutive pre-mRNA splicing and in alternative splicing regulation. Using profile analysis we constructed a database enriched in protein sequences containing one or more presumptive copies of the RNA-recognition motif (RRM). We provide an accurate alignment of RRMs and structure-based criteria for identifying new RRMs, including many that lack the prototype RNP-1 submotif. We present a comprehensive table of 125 sequences containing 252 RRMs, including 22 previously unreported RRMs in 17 proteins. The presence of a putative RRM in these proteins, which are implicated in a variety of cellular processes, strongly suggests that their function involves binding to RNA. Unreported homologies in the RRM-enriched database to the metazoan SR family of splicing factors are described for an Arg-rich human nuclear protein and two yeast proteins (S. pombe mei2 and S. cerevisiae Npl3). We have rigorously tested the phylogenetic relationships of a large sample of RRMs. This analysis indicates that the RRM is an ancient conserved region (ACR) that has diversified by duplication of genes and intragenic domains. Statistical analyses and classification of repeated Arg-Ser (RS) and RGG domains in various protein splicing factors are presented.
663 citations
TL;DR: A chronology of key events and events leading to the formation of the HJ-Uridine Incorporation, In Situ Nick Translation, and subsequent efforts to correct for these errors.
Abstract: DNA REPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 TRANSCRIPTION AND PRE-mRNA PROCESSING .... . . ) ....... ,.... 279 Localization of Transcriptionally Active Nuclear Regions by [ HJ-Uridine Incorporation or In Situ Nick Translation . . . . . . . . . . . . . . . . 279 Pre-mRNA Splicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 An Arginine/Serine-Rich Domain Targets Proteins to Nuclear Speckles . . . . . . 284 Effect of RNA Polymerase II Transcription on the Localization of Splicing Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,.... 285 Distribution of hnRNP Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Localization of Splicing Factors in the Amphibian Germinal Vesicle . . . . . . . . 289 Localization of Splicing Factors in Yeast 290 Distribution of Poly(A)'t RNA . . . . . . ... . . . . ..... . ..... . . . . .... 291 Distribution of Specific Cellular Transcripts . . . . . . . . . . . . . . . . . . . . . . . 291 NUCLEOLAR ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
617 citations
TL;DR: In this paper, the authors used a Saccharomyces cerevisiae genetic system to detect the physical interaction of RAS and RAF oncoproteins and found that the interaction required only the N-terminal domains of RAF or byr2.
Abstract: We used a Saccharomyces cerevisiae genetic system to detect the physical interaction of RAS and RAF oncoproteins. We also observed interaction between RAS and byr2, a protein kinase implicated as a mediator of the Schizosaccharomyces pombe ras1 protein. Interaction with RAS required only the N-terminal domains of RAF or byr2 and was disrupted by mutations in either the guanine nucleotide-binding or effector-loop domains of RAS. We observed interaction between MEK (a kinase that phosphorylates mitogen-activated protein kinases) and the catalytic domain of RAF. RAS and MEK also interacted but only when RAF was overexpressed.
589 citations
TL;DR: It is shown that overexpression of Grb2 potentiates the EGF-induced activation of Ras and mitogen-activated protein kinase by enhancing the rate of guanine nucleotide exchange on Ras.
Abstract: Activation of receptor tyrosine kinases such as those for epidermal growth factor (EGF), platelet-derived growth factor, or nerve growth factor converts the inactive, GDP-bound form of Ras to the active, GTP-bound form, and a dominant negative mutant of Ras interferes with signalling from such receptors. The mechanisms by which receptor tyrosine kinases and Ras are coupled, however, are not well understood. Many cytoplasmic proteins regulated by such receptors contain Src-homology (SH) 2 and 3 domains, and the SH2- and SH3-containing protein Grb2, like its homologue from Caenorhabditis elegans, Sem-5, appears to play an important role in the control of Ras by receptor tyrosine kinases. Here we show that overexpression of Grb2 potentiates the EGF-induced activation of Ras and mitogen-activated protein kinase by enhancing the rate of guanine nucleotide exchange on Ras. Cellular Grb2 appears to form a complex with a guanine-nucleotide-exchange factor for Ras, which binds to the ligand-activated EGF receptor, allowing the tyrosine kinase to modulate Ras activity.
TL;DR: It is proposed that Cln3 may be an upstream activator of the G1 cyclins which directly catalyze Start, and given the large number of known cyclins, such cyclin cascades may be a common theme in cell cycle control.
Abstract: In the budding yeast Saccharomyces cerevisiae, the G1 cyclins Cln1, Cln2 and Cln3 regulate entry into the cell cycle (Start) by activating the Cdc28 protein kinase. We find that Cln3 is a much rarer protein than Cln1 or Cln2 and has a much weaker associated histone H1 kinase activity. Unlike Cln1 and Cln2, Cln3 is not significantly cell cycle regulated, nor is it down-regulated by mating pheromone-induced G1 arrest. An artificial burst of CLN3 expression early in G1 phase accelerates Start and rapidly induces at least five other cyclin genes (CLN1, CLN2, HCS26, ORFD and CLB5) and the cell cycle-specific transcription factor SWI4. In similar experiments, CLN1 is less efficient than CLN3 at activating Start. Strikingly, expression of HCS26, ORFD and CLB5 is dependent on CLN3 in a cln1 cln2 strain, possibly explaining why CLN3 is essential in the absence of CLN1 and CLN2. To explain the potent ability of Cln3 to activate Start, despite its apparently weak biochemical activity, we propose that Cln3 may be an upstream activator of the G1 cyclins which directly catalyze Start. Given the large number of known cyclins, such cyclin cascades may be a common theme in cell cycle control.
TL;DR: The tyrosine phosphorylation events on Stat and Jak proteins after treatment of cells with IFNs α and γ and with epidermal growth factor (EGF) are investigated and Jakl is found to be the enzyme that phosphorylates Tyr701inStat91.
Abstract: Binding of interferons IFN-alpha and IFN-gamma to their cell surface receptors promptly induces tyrosine phosphorylation of latent cytoplasmic transcriptional activators (or Stat proteins, for signal transducers and activators of transcription). Interferon-alpha activates both Stat91 (M(r) 91,000; ref. 1) and Stat113 (M(r) 113,000; ref. 2) whereas IFN-gamma activates only Stat91 (refs 3, 4). The activated proteins then move into the nucleus and directly activate genes induced by IFN-alpha and IFN-gamma. Somatic cell genetics experiments have demonstrated a requirement for tyrosine kinase-2 (Tyk2) in the IFN-alpha response pathway and for Jak2 (ref. 6), a kinase with similar sequence, in the IFN-gamma response pathway. Here we investigate the tyrosine phosphorylation events on Stat and Jak proteins after treatment of cells with IFNs alpha and gamma and with epidermal growth factor (EGF). Stat91 is phosphorylated on Tyr701 after cells are treated with IFN-alpha and EGF, as it was after treatment with IFN-gamma (ref. 8). We find that Jak1 also becomes phosphorylated on tyrosine after cells are treated with these same three ligands, although each ligand is shown to activate at least one other different kinase. Jak1 may therefore be the enzyme that phosphorylates Tyr 701 in Stat91.
TL;DR: Characterization of a temperature-sensitive mutation in the gene encoding the 72-kD subunit of ORC (ORC2) indicates that this protein complex functions early in the DNA replication process, and supports the hypothesis that ORC acts as an initiator protein at yeast origins of DNA replication and suggests that OrC also functions in the determination of transcriptional domains.
Abstract: The genes encoding two of the subunits of the Saccharomyces cerevisiae origin recognition complex (ORC) have been isolated. Characterization of a temperature-sensitive mutation in the gene encoding the 72-kD subunit of ORC (ORC2) indicates that this protein complex functions early in the DNA replication process. Moreover, ORC derived from orc2ts cells is defective for DNA binding. Others have shown a defect in orc2ts cells in transcriptional silencing at the silent mating-type loci. Consistent with this finding, ORC specifically binds to each of the four mating-type silencers identified in yeast. These findings support the hypothesis that ORC acts as an initiator protein at yeast origins of DNA replication and suggest that ORC also functions in the determination of transcriptional domains.
TL;DR: It is found that the CLBs play a central role in the transition from CLNs to CLBs: theCLBs stimulate their own expression while repressing that of CLNs.
TL;DR: The crystal structure of the DNA (cytosine-5)-methyltransferase, M.Hhal (recognition sequence: GCGC), complexed with S-adenosyl-l-methionine has been determined and refined at 2.5 A resolution.
TL;DR: Results indicate that SH3 domains are responsible for the targeting of signaling molecules to specific subcellular locations in PLC-gamma and GRB2.
TL;DR: It is suggested that PKA plays a crucial role in the cAMP cascade in mushroom bodies to mediate learning and memory processes.
TL;DR: Four human genes (DPDE1 through DPDE4) closely related to the dnc learning and memory locus of Drosophila melanogaster are isolated and shown to encode cyclic AMP-specific phosphodiesterases.
Abstract: We have isolated cDNAs for four human genes (DPDE1 through DPDE4) closely related to the dnc learning and memory locus of Drosophila melanogaster. The deduced amino acid sequences of the Drosophila and human proteins have considerable homology, extending beyond the putative catalytic region to include two novel, highly conserved, upstream conserved regions (UCR1 and UCR2). The upstream conserved regions are located in the amino-terminal regions of the proteins and appear to be unique to these genes. Polymerase chain reaction analysis suggested that these genes encoded the only homologs of dnc in the human genome. Three of the four genes were expressed in Saccharomyces cerevisiae and shown to encode cyclic AMP-specific phosphodiesterases. The products of the expressed genes displayed the pattern of sensitivity to inhibitors expected for members of the type IV, cyclic AMP-specific class of phosphodiesterases. Each of the four genes demonstrated a distinctive pattern of expression in RNA from human cell lines.
TL;DR: This work highlights parallels between the control of phenotypic expression in the nervous and hematopoietic systems and between the cytokines involved in the immune response and the response of the nervous system to injury and a potential role for cytokines in synaptic plasticity.
TL;DR: It is reported here that although alone NO has no evident effect on transcription, it can act as an amplifier of calcium signals in neuronal cells, and induction of gene activity following NO-amplified calcium action involves protein kinase A-dependent activation of the transcription factor CREB.
Abstract: NITRIC oxide (NO) is a short-lived, highly reactive gas, which has been identified as a mediator in vasodilation, an active agent in macrophage cytotoxicity and neurotoxicity, and a neurotransmitter in the central and peripheral nervous systems1–5. Production of NO by neurons is critical for facilitated synaptic transmission in models of synaptic plasticity such as long-term potentiation and long-term depression, suggesting a role for NO as a retrograde messenger that could complete a hypothetical feedback loop by strengthening the connection between postsynaptic and presynaptic cells6–10. We report here that although alone NO has no evident effect on transcription, it can act as an amplifier of calcium signals in neuronal cells. NO and Ca2+ action have to coincide in time for amplification to occur. Experiments with a series of simplified reporter genes in combination with specific recombinant protein kinase inhibitors suggest that induction of gene activity following NO-amplified calcium action involves protein kinase A-dependent activation of the transcription factor CREB.
TL;DR: The observations from transgenic mice suggest that nef‐elicited perturbations in T cell signalling play an important role in the viral life cycle in vivo, perhaps resulting in elimination of infected CD4+ T cells.
Abstract: The nef gene, which encodes related cytoplasmic proteins in both human (HIV) and simian (SIV) immunodeficiency viruses is dispensable for viral replication in vitro. In contrast, in vivo experiments have revealed that SIV nef is required for efficient viral replication and development of AIDS in SIV infected rhesus monkeys, thus indicating that nef plays an essential role in the natural infection. We show that expression of the Nef protein from the HIV-1 NL43 isolate in transgenic mice perturbs development of CD4+ T cells in the thymus and elicits depletion of peripheral CD4+ T cells. Thymic T cells expressing NL43 Nef show altered activation responses. In contrast, Nef protein of the HIV-1 HxB3 isolate does not have an overt effect on T cells when expressed in transgenic animals. The differential effects of the two HIV-1 nef alleles in transgenic mice correlate with down-regulation of CD4 antigen expression on thymic T cells. The differential interactions of the NL43 and HxB3 nef alleles with CD4 were reproduced in a transient assay in human CD4+ CEM T cells. Down-regulation of CD4 by nef in both human and transgenic murine T cells indicates that the relevant interactions are conserved in these two systems and suggests that the consequences of Nef expression on the host cell function can be analyzed in vivo in the murine system. Our observations from transgenic mice suggest that nef-elicited perturbations in T cell signalling play an important role in the viral life cycle in vivo, perhaps resulting in elimination of infected CD4+ T cells.
TL;DR: Although sequences outside of the central region of p53 contribute to both nonspecific DNA- binding and oligomerization, they are not required for sequence-specific DNA-binding.
Abstract: p53 is a sequence-specific DNA-binding oligomeric protein that can activate transcription from promoters bearing p53-binding sites. Whereas the activation region of p53 has been identified within the amino terminus, the location of the specific DNA-binding domain has not been reported. Thermolysin treatment of p53 protein generates a stable protease-resistant fragment that binds with marked specificity to p53 DNA-binding sites. Amino-terminal sequencing of the fragment located the thermolysin cleavage site to residue 91. Because the fragment does not contain the cdc2 phosphorylation site at Ser-315, we conclude that the the site-specific DNA-binding domain of p53 spans the central region of the protein. The vast majority of the mutations in oncogenically derived p53 proteins are located within this central portion of the molecule. Such mutant p53 proteins exhibit defective sequence-specific DNA-binding. Although thermolysin digestion of mutant p53 proteins generates proteolytic patterns that differ from wild-type protein, one mutant tested, His-273, generates a resistant fragment that migrates with a similar electrophoretic mobility to the wild-type protease-resistant fragment. Interestingly, although intact mutant His-273 protein binds to DNA at 20 degrees C, the thermolysin-resistant mutant fragment does not. In addition, the central protease-resistant, site-specific binding region of wild-type p53 does not demonstrate nonspecific DNA-binding. Thus, although sequences outside of the central region of p53 contribute to both nonspecific DNA-binding and oligomerization, they are not required for sequence-specific DNA-binding.
TL;DR: Results suggest that the ligand for this transmembrane PTPase is another PTPmu molecule on an adjacent cell, and homophilic binding interactions may be an important component of the function of P TPmu in vivo.
Abstract: The receptor-like protein tyrosine phosphatase, PTPmu, displays structural similarity to cell-cell adhesion molecules of the immunoglobulin superfamily. We have investigated the ability of human PTPmu to function in such a capacity. Expression of PTPmu, with or without the PTPase domains, by recombinant baculovirus infection of Sf9 cells induced their aggregation. However, neither a chimeric form of PTPmu, containing the extracellular and transmembrane segments of the EGF receptor and the intracellular segment of PTPmu, nor the intracellular segment of PTPmu expressed as a soluble protein induced aggregation. PTPmu mediates aggregation via a homophilic mechanism, as judged by lack of incorporation of uninfected Sf9 cells into aggregates of PTPmu-expressing cells. Homophilic binding has been demonstrated between PTPmu-coated fluorescent beads (Covaspheres) and endogenously expressed PTPmu on MvLu cells. Additionally the PTPmu-coated beads specifically bound to a bacterially expressed glutathione-S-transferase fusion protein containing the extracellular segment of PTPmu (GST/PTPmu) adsorbed to petri dishes. Covaspheres coated with the GST/PTPmu fusion protein aggregated in vitro and also bound to PTPmu expressed endogenously on MvLu cells. These results suggest that the ligand for this transmembrane PTPase is another PTPmu molecule on an adjacent cell. Thus homophilic binding interactions may be an important component of the function of PTPmu in vivo.
TL;DR: A combination of site-directed point mutagenesis and monoclonal antibody competition experiments reported here suggests that p300 binding is dependent on specific, conserved residues in the N terminus, including positively charged residues at positions 2 and 3 of the E1A proteins, and that p 300 and pRB bind to distinct, nonoverlapping subregions within conserved region 1.
Abstract: Adenovirus early region 1A (E1A) oncogene-encoded sequences essential for transformation- and cell growth-regulating activities are localized at the N terminus and in regions of highly conserved amino acid sequence designated conserved regions 1 and 2. These regions interact to form the binding sites for two classes of cellular proteins: those, such as the retinoblastoma gene product, whose association with the E1A products is specifically dependent on region 2, and another class which so far is known to include only a large cellular DNA-binding protein, p300, whose association with the E1A products is specifically dependent on the N-terminal region. Association between the E1A products and either class of cellular proteins can be disrupted by mutations in conserved region 1. While region 2 has been studied intensively, very little is known so far concerning the nature of the essential residues in the N-terminal region, or about the manner in which conserved region 1 participates in the binding of two distinct sets of cellular proteins. A combination of site-directed point mutagenesis and monoclonal antibody competition experiments reported here suggests that p300 binding is dependent on specific, conserved residues in the N terminus, including positively charged residues at positions 2 and 3 of the E1A proteins, and that p300 and pRB bind to distinct, nonoverlapping subregions within conserved region 1. The availability of precise point mutations disrupting p300 binding supports previous data linking p300 with cell cycle control and enhancer function.
TL;DR: These data suggest a recruiting mechanism that regulates the localization of transcription and splicing factors in response to the initiation of active transcription, and demonstrate a very close association between RNA transcripts and transcription and pre-mRNAsplicing factors.
TL;DR: It is proposed that in some cases the ratio of SF2/ASF to hnRNP A1 may play a role in regulating alternative splicing by exon inclusion or skipping through the antagonistic effects of these proteins on alternative splice site selection.
Abstract: The essential splicing factor SF2/ASF and the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) modulate alternative splicing in vitro of pre-mRNAs that contain 5' splice sites of comparable strengths competing for a common 3' splice site. Using natural and model pre-mRNAs, we have examined whether the ratio of SF2/ASF to hnRNP A1 also regulates other modes of alternative splicing in vitro. We found that an excess of SF2/ASF effectively prevents inappropriate exon skipping and also influences the selection of mutually exclusive tissue-specific exons in natural beta-tropomyosin pre-mRNA. In contrast, an excess of hnRNP A1 does not cause inappropriate exon skipping in natural constitutively or alternatively spliced pre-mRNAs. Although hnRNP A1 can promote alternative exon skipping, this effect is not universal and is dependent, e.g., on the size of the internal alternative exon and on the strength of the polypyrimidine tract in the preceding intron. With appropriate alternative exons, an excess of SF2/ASF promotes exon inclusion, whereas an excess of hnRNP A1 causes exon skipping. We propose that in some cases the ratio of SF2/ASF to hnRNP A1 may play a role in regulating alternative splicing by exon inclusion or skipping through the antagonistic effects of these proteins on alternative splice site selection.
TL;DR: The activation by EGF of a DNA-binding protein in a cell-free system where activation of DNA binding requires ligand, receptor, ATP and phosphotyrosine–SH2 interactions is reported.
Abstract: GROWTH factors such as platelet-derived growth factor and epidermal growth factor (EGF) bind to and activate cell-surface receptors with intrinsic tyrosine kinase activities1. Receptor activation elicits multiple physiological changes in target cells, including alterations in gene expression2–4. Receptor tyrosine kinase signalling involves recruitment of proteins into a signalling complex through interactions between receptor autophosphorylation sites and the src-homology region-2 (SH2) domains on these signalling proteins5–9. Diverse signals can subsequently be generated, depending on the specific receptor and cell type2,10. How such signals are transmitted to the nucleus is poorly understood, but because the transcriptional activation of many genes by growth factors occurs in the absence of new protein synthesis4, one or more signals emanating from growth factor receptors must directly affect transcription factors. We report here the activation by EGF of a DNA-binding protein in a cell-free system where activation of DNA binding requires ligand, receptor, ATP and phosphotyrosine–SH2 interactions.