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At least 937 records · Page 52Linked to original sources
PubMed2005

A splicing repressor domain in polypyrimidine tract-binding protein.

Polypyrimidine tract-binding protein (PTB) is an hnRNP with four RRM type domains. It plays roles as a repressive alternative splicing regulator of multilple target genes, as well as being involved in pre-mRNA 3' end processing, mRNA localization, stability, and internal ribosome entry site-mediated translation. Here we have used a tethered function assay, in which a fusion protein of PTB and the bacteriophage MS2 coat protein is recruited to a splicing regulatory site by binding to an artificially inserted MS2 binding site. Deletion mutations of PTB in this system allowed us to identify RRM2 and the following inter-RRM linker region as the minimal region of PTB that can act as splicing repressor domain when recruited to RNA. Splicing repression by the minimal repressor domain remained cell type-specific and dependent upon other defined regulatory elements in the alpha-tropomyosin test minigene. Our results highlight the fact that splicing repression by PTB can be uncoupled from the mode by which it binds to RNA.

Alternative Splicing↗
PubMed2000

Analysis of Groucho-histone interactions suggests mechanistic similarities between Groucho- and Tup1-mediated repression.

The Drosophila Groucho (Gro) protein is the defining member of a family of metazoan corepressors that have roles in many aspects of development, including segmentation, dorsal/ventral pattern formation, Notch signaling, and Wnt/Wg signaling. Previous speculation has suggested that Gro may be orthologous to the yeast corepressor Tup1. In support of this idea, a detailed alignment between the C-terminal WD-repeat domains of these two proteins shows that each Gro WD repeat is most similar to the Tup1 WD repeat occupying the corresponding position in that protein. Our analysis of Gro-histone interactions provides further support for a close evolutionary relationship between Gro and Tup1. In particular, we show that, as with the N-terminal region of Tup1, the N-terminal region of Gro is necessary and sufficient for direct binding to histones. The highest affinity interaction is with histone H3 and binding is primarily observed with hypoacetylated histones. Using transient transfection assays, we show that a Gal4-Gro fusion protein containing the histone-binding domain is able to repress transcription. Deletions that weaken histone binding also weaken repression. These findings, along with our recent report that Gro interacts with the histone deacetylase Rpd3, suggest a mechanism for Gro-mediated repression.

Acetylation↗
PubMed1998

The BCL-6 POZ domain and other POZ domains interact with the co-repressors N-CoR and SMRT.

Virtually all diffuse large cell lymphomas and a significant fraction of follicular lymphomas contain translocations and/or point mutations in the 5' non-coding region of the putative oncogene BCL-6, that are presumed to deregulate its expression. BCL-6 encodes a Cys2-His2 zinc finger transcriptional repressor with a POZ domain at its amino-terminus. The POZ (or BTB) domain, a 120-amino-acid motif, mediates homomeric and, in some proteins, heteromeric POZ-POZ interactions. In addition, the POZ domain is required for transcriptional repression of several proteins, including BCL-6. Using a yeast two-hybrid screen, we identified N-CoR and SMRT as BCL-6 interacting proteins. Both N-CoR and SMRT, which were originally identified as co-repressors for the unliganded nuclear thyroid hormone and retinoic acid receptors, are components of large complexes containing histone deacetylases. We show that the interaction between BCL-6 and these co-repressors is also detected in the more physiologically relevant mammalian two-hybrid assay. The POZ domain is necessary and sufficient for interaction with these co-repressors. BCL-6 and N-CoR co-localize to punctate regions of the nucleus. Furthermore, when BCL-6 is bound to its consensus recognition sequence in vivo, it can interact with N-CoR and SMRT. We find, in vitro, that POZ domains from a variety of other POZ domain-containing proteins, including the transcriptional repressor PLZF, as well as ZID, GAGA and a vaccinia virus protein, SalF17R, also interact with varying affinities with N-CoR and SMRT. We find that BCL-6 POZ domain mutations that disrupt the interaction with N-CoR and SMRT no longer repress transcription. In addition, these mutations no longer self associate suggesting that self interaction is required for interaction with the co-repressors and for repression. More recently N-CoR has also been implicated in transcriptional repression by the Mad/Mxi proteins. Our demonstration that N-CoR and SMRT interact with the POZ domain containing proteins indicates that these co-repressors are likely involved in the mediation of repression by multiple classes of repressors and may explain, in part, how POZ domain containing repressors mediate transcriptional repression.

Amino Acid Sequence↗
PubMed2001

p53-dependent transcriptional repression of p21(waf1) by hepatitis C virus NS3.

Hepatitis C virus (HCV) NS3 protein is known to affect normal cellular functions, such as cell proliferation and cell death, and to be involved, either directly or indirectly, in HCV hepatocarcinogenesis. In this study, we demonstrated that NS3 protein could specifically repress the promoter activity of p21 in a dose-dependent manner. The effect was not cell type-specific and was synergistic when combined with HCV core protein. Repression of the p21 promoter by NS3 was almost completely lost when p53 binding sites present on the p21 promoter were removed. Furthermore, p53 binding sites were sufficient to confer a strong NS3 responsiveness to an heterologous promoter, suggesting that NS3 represses the transcription of p21 by modulating the activity of p53. Although the NS3 protein domain required for the majority of p21 repression was located on the protease domain, the proteinase activity itself does not seem to be necessary for repression. Both transcription and protein stability of p53 were unaffected by NS3, suggesting that NS3 might repress transcription of p21 by inhibiting the regulatory activity of p53 via protein-protein interaction(s). Finally, the growth rate of NS3-expressing cell lines was at least twice as fast as that of the parent NIH 3T3 cells, indicating that the repression of p21 is actually reflected by the stimulation of cell growth.

3T3 Cells↗
PubMed2004

Mbd1 is recruited to both methylated and nonmethylated CpGs via distinct DNA binding domains.

MBD1 is a vertebrate methyl-CpG binding domain protein (MBD) that can bring about repression of methylated promoter DNA sequences. Like other MBD proteins, MBD1 localizes to nuclear foci that in mice are rich in methyl-CpG. In methyl-CpG-deficient mouse cells, however, Mbd1 remains localized to heterochromatic foci whereas other MBD proteins become dispersed in the nucleus. We find that Mbd1a, a major mouse isoform, contains a CXXC domain (CXXC-3) that binds specifically to nonmethylated CpG, suggesting an explanation for methylation-independent localization. Transfection studies demonstrate that the CXXC-3 domain indeed targets nonmethylated CpG sites in vivo. Repression of nonmethylated reporter genes depends on the CXXC-3 domain, whereas repression of methylated reporters requires the MBD. Our findings indicate that MBD1 can interpret the CpG dinucleotide as a repressive signal in vivo regardless of its methylation status.

Alternative Splicing↗
PubMed2005

The nuclear-envelope protein and transcriptional repressor LAP2beta interacts with HDAC3 at the nuclear periphery, and induces histone H4 deacetylation.

Nuclear-envelope proteins have been implicated in diverse and fundamental cell functions, among them transcriptional regulation. Gene expression at the territory of the nuclear periphery is known to be repressed by epigenetic modifications such as histone deacetylation and methylation. However, the mechanism by which nuclear-envelope proteins are involved in such modifications is still obscure. We have previously shown that LAP2beta, an integral nuclear-envelope protein that contains the chromatin-binding LEM domain, was able to repress the transcriptional activity of the E2F5-DP3 heterodimer. Here, we show that LAP2beta's repressive activity is more general, encompassing various E2F members as well as other transcription factors such as p53 and NF-kappaB. We further show that LAP2beta interacts at the nuclear envelope with HDAC3, a class-I histone deacetylase, and that TSA (an HDAC inhibitor) abrogates LAP2beta's repressive activity. Finally, we show that LAP2beta is capable of inducing histone-H4 deacetylation. Our data provide evidence for the existence of a previously unknown repressive complex, composed of an integral nuclear membrane protein and a histone modifier, at the nuclear periphery.

Cell Line, Tumor↗
PubMed1995

Negative cross-talk between RelA and the glucocorticoid receptor: a possible mechanism for the antiinflammatory action of glucocorticoids.

Glucocorticoids are efficient antiinflammatory agents, and their effects include transcriptional repression of several cytokines and adhesion molecules. Whereas glucocorticoids down-regulate the expression of genes relevant during inflammation, nuclear factor (NF)-kappa B/Rel proteins function as important positive regulators of these genes. The expression of intercellular adhesion molecule-1 (ICAM-1), which plays an essential role in recruitment and migration of leukocytes to sites of inflammation, is also down-regulated by glucocorticoids. We found that a functional NF-kappa B site in the ICAM-1 promoter, which can be activated by either 12-O-tetradecanoylphorbol-13-acetate or tumor necrosis factor-alpha (TNF alpha), is also the target for glucocorticoids. In this report we present evidence that the ligand-activated glucocorticoid receptor (GR) is able to repress RelA-mediated activation of the ICAM-1 NF-kappa B site. Conversely, transcriptional activation by GR via a glucocorticoid response element is specifically repressed by RelA, but not by other NF-kappa B/Rel family members. Mutational analysis of GR demonstrates that the DNA binding domain and the ligand binding domain are required for the functional repression of NF-kappa B activation. Despite the importance of the DNA binding domain, we found that the transcriptional repression of NF-kappa B, mediated by GR, is not caused by binding of GR to the ICAM-1 NF-kappa B element, but by a physical interaction between the GR and RelA protein. The repressive effect of GR on NF-kappa B-mediated activation was not shared by other steroid/thyroid receptors. Only the progesterone receptor, which belongs to the same subfamily as GR and which possesses high homology with GR, was able to repress NF-kappa B-mediated transcription. These studies highlight a possible molecular mechanism that can explain the antiinflammatory effects of glucocorticoid treatment during inflammation.

Amino Acid Sequence↗
PubMed1999

Transcriptional repression by REST: recruitment of Sin3A and histone deacetylase to neuronal genes.

Many genes whose expression is restricted to neurons in the brain contain a silencer element (RE1/NRSE) that limits transcription in nonneuronal cells by binding the transcription factor REST (also named NRSF or XBR). Although two independent domains of REST are known to confer repression, the mechanisms of transcriptional repression by REST remain obscure. We provide multiple lines of evidence that the N-terminal domain of REST represses transcription of the GluR2 and type II sodium-channel genes by recruiting the corepressor Sin3A and histone deacetylase (HDAC) to the promoter region in nonneuronal cells. These results identify a general mechanism for controlling the neuronal expression pattern of a specific set of genes via the RE1 silencer element.

Acetylation↗
PubMed1999

Resistance to pseudorabies virus infection in transgenic mice expressing the chimeric transgene that represses the immediate-early gene transcription.

A chimeric gene encoding a fusion protein consisting of the DNA-binding domain of the immediate-early (IE) protein of pseudorabies virus (PRV) and a tail-truncated VP16 of herpes simplex virus 1, lacking the transcription activation domain, has been shown to repress transcription of the PRV IE gene, resulting in the inhibition of PRV growth in vitro. To assess the antiviral potential of the fusion protein in vivo, transgenic mice containing the chimeric gene under the control of the virus- and interferon-inducible Mx 1 promoter were generated. A transgenic mouse line showed marked resistance to PRV infection when the mice were challenged intranasally with PRV. Inhibition of PRV replication was also observed in monolayers of embryonic cells prepared from the transgenic mice. In the cells infected with PRV, transcription of the PRV IE gene was repressed. The present results indicate that the chimeric gene is able to exert a significant antiviral effect against PRV infection in vivo.

Animals↗
PubMed2002

Nuclear architecture and spatial positioning help establish transcriptional states of telomeres in yeast.

Recent experiments have shown that gene repression can be correlated with relocation of genes to heterochromatin-rich silent domains. Here, we investigate whether nuclear architecture and spatial positioning can contribute directly to the transcriptional activity of a genetic locus in Saccharomyces cerevisiae. By disassembling telomeric silent domains without altering the chromatin-mediated silencing machinery, we show that the transcriptional activity of silencer--reporter constructs depends on intranuclear position. This demonstrates that telomeric silent domains are actively involved in transcriptional silencing. Employing fluorescent in situ hybridization (FISH) in combination with genetic assays, we demonstrate that telomeres control the establishment of transcriptional states by reversible partitioning with the perinuclear silencing domains. Anchoring telomeres interferes with their ability to assume an active state, whereas disassembly of silencing domains prevents telomeres from assuming a repressed state. Our data support a model in which domains of enriched transcriptional regulators allow genes to determine transcriptional states by spatial positioning.

Cell Nucleus↗
PubMed2002

Mutation in domain II of IAA1 confers diverse auxin-related phenotypes and represses auxin-activated expression of Aux/IAA genes in steroid regulator-inducible system.

Most of Aux/IAA genes are rapidly induced by auxin. The Aux/IAA proteins are short-lived nuclear proteins sharing the four conserved domains. Domain II is critical for rapid degradation of Aux/IAA proteins. Among these gene family members, IAA1 is one of the earliest auxin-inducible genes. We used a steroid hormone-inducible system to reveal putative roles and downstream signaling of IAA1 in auxin response. Arabidopsis transgenic plants were generated expressing fusion protein of IAA1 (IAA1-GR) or IAA1 with a mutation in domain II (iaa1-GR) and the glucocorticoid hormone-binding domain (GR). IAA1-GR transgenic plants did not exhibit any discernable phenotypic differences by DEX treatment that allows nuclear translocation of the fusion protein. In contrast, diverse auxin-related physiological processes including gravitropism and phototropism were impaired by DEX treatment in roots, hypocotyls, stems, and leaves in iaa1-GR transgenic plants. Auxin induction of seven Aux/IAA mRNAs including IAA1 itself was repressed by DEX treatment, suggesting that IAA1 functions in the nucleus by mediating auxin response and might act as a negative feedback regulator for the expression of Aux/IAA genes including IAA1 itself. Auxin induction of Aux/IAA genes in the presence of cycloheximide can be repressed by DEX treatment, showing that the repression of transcription of the Aux/IAAs by the iaa1 mutant protein is primary. Wild-type IAA1-GR could not suppress auxin induction of IAA1 and IAA2. These results indicate that inhibition of auxin-activated transcription of Aux/IAA genes by the iaa1 mutant protein might be responsible for alteration of various auxin responses.

Arabidopsis↗
PubMed1993

The interplay between multiple enhancer and silencer elements defines the pattern of decapentaplegic expression.

The product of the zygotically active decapentaplegic (dpp) gene appears to function as a morphogen that specifies positional information in the dorsal half of the Drosophila embryo. The dorsal-specific transcription of dpp is the key step in establishing a morphogen gradient. We demonstrate here that multiple regions within the second intron of the gene cooperate with one another to generate the wild-type level and pattern of dpp transcription. These regions contain both generalized enhancer elements as well as ventral-specific repressor elements. Placed within the context of heterologous promoters, the intron retains its ability to direct general activation and ventral repression. The ventral specific repression of dpp transcription is directly mediated by binding sites for the dorsal (dl) morphogen in the repressor elements. In contrast with the zerknüllt (zen) ventral repressor element, which contains a few high-affinity dl-binding sites, dpp contains multiple relatively low-affinity sites that function together to bring about complete ventral repression. Because dpp and zen have nearly coincident early expression domains, these results indicate that the same boundary of repression can be specified by dl-binding sites of different affinity. We discuss the possibility that unknown factors interact with dl protein to determine the domain of dl-mediated repression.

Animals↗
PubMed2002

An inhibitor of c-jun aminoterminal kinase (SP600125) represses c-Jun activation, DNA-binding and PMA-inducible 92-kDa type IV collagenase expression.

The 92-kDa type IV collagenase (MMP-9) contributes to tumor invasion and metastases and strategies to down-regulate its expression could ultimately be of clinical utility. Although the expression of this collagenase is regulated by numerous growth factors, the signaling pathways that transduce these signals are fewer in number and therefore represent pharmacological targets. In this regard, we previously reported that MMP-9 expression was regulated by the c-jun amino terminal kinase (JNK) signaling cascade. Therefore, we undertook a study to determine the efficacy of a novel compound (SP600125), which binds to the ATP binding site of all known JNKs, in repressing MMP-9 expression. In OVCAR-3 cells, SP600125 inhibited the PMA-dependent secretion of MMP-9 in a time-dependent manner and over a dose range that blocked c-Jun phosphorylation and AP-1 binding. SP600125 repressed the activity of a PMA-stimulated MMP-9 promoter-driven luciferase reporter, suggesting that diminished secretion of this collagenase reflected reduced transcription. Further, the activity of a GAL4-driven reporter in PMA-treated cells, co-transfected with an expression construct encoding the trans-activation domain of c-Jun fused to the DNA binding domain of GAL4, was repressed by SP600125. These findings indicate the efficacy of SP600125 in inhibiting c-Jun activation, DNA-binding and the PMA-dependent induction of MMP-9 expression.

Anthracenes↗
PubMed2004

Mitotic cyclins stimulate the activity of c-Myb-like factors for transactivation of G2/M phase-specific genes in tobacco.

Myb transcription factors, which contain three imperfect repeats in the Myb domain, are evolutionarily conserved members of the Myb superfamily. Vertebrate Myb proteins with three repeats, c-Myb, A-Myb, and BMyb, play important roles at the G(1)/S transition in the cell cycle. In plants, this type of Myb protein controls the G(2)/M phase by activating or repressing the transcription of cyclin B genes and a variety of other G(2)/M phase-specific genes. In tobacco, two genes for Myb activators, NtmybA1 and NtmybA2, are transcriptionally controlled and are expressed specifically at the G(2)/M phase. As we showed here, in addition to the control at the transcriptional level, activity of NtmybA2 is also controlled at the post-translational level. We found that the transactivation potential of NtmybA2 is repressed by a regulatory domain located at its carboxyl terminus and that specific classes of cyclins A and B enhanced NtmybA2 activity possibly by relieving this inhibitory effect. Mutations at the 20 potential sites of phosphorylation by cyclin-dependent kinase (CDK) in NtmybA2 blocked the enhancing effects of the cyclins on NtmybA2 activity. Recombinant NtmybA2 was phosphorylated in vitro by a CDK fraction prepared from tobacco BY2 cells. The kinase activity for NtmybA2 in the CDK fraction was cell cycle-regulated in BY2 cells, peaking at the G(2)/M phase when the level of transcripts of cyclin B is maximal. Taken together, our data suggest that NtmybA2 is phosphorylated by a specific cyclin/CDK complex(es) at G(2)/M and that this phosphorylation removes the inhibitory effect of its C-terminal region, thereby activating NtmybA2 specifically at G(2)/M.

Binding Sites↗
PubMed1995

Stress-activated protein kinases bind directly to the delta domain of c-Jun in resting cells: implications for repression of c-Jun function.

The transactivating function of the c-Jun proto-oncogene component of the AP-1 transcription factor is acutely regulated by a wide variety of cellular signals via modulation of phosphorylation of two serines (63 and 73). The viral oncoprotein, v-Jun, while containing homologous serines, is not phosphorylated in cells. A novel family of stress-activated protein kinases (SAPKs), also termed Jun N-terminal domain kinases (JNKs), are responsible for mediating S63/73 phosphorylation in response to a variety of cellular stimuli including tumor necrosis factor-alpha, heat stress and u.v. light. The p54 alpha 1, alpha 2, p54 beta and p46 beta SAPKs are shown to bind directly to c-Jun but not to v-Jun, with an absolute requirement for c-Jun amino acids 31-47, a region deleted in v-Jun. Inactive SAPKs tightly bind c-Jun in resting cells and may be a manifestation of the 'delta' inhibitor, a previously described repressor of c-Jun function.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1998

Identification of amino acid residues of Gsalpha critical to repression of adipogenesis.

Gsalpha regulates the differentiation of 3T3-L1 mouse embryonic fibroblasts to adipocytes, a process termed adipogenesis. Through the expression of chimera created by substituting regions of Gsalpha with corresponding regions of the G protein Gialpha2, the domain of Gsalpha involved in repression of adipogenesis was localized to sequence 146-235 of the molecule (Wang, H-y., Johnson, G. L., Liu, X. , Malbon, C. C. (1996) J. Biol. Chem. 271, 22022-22029). As a prelude to alanine-scanning mutagenesis, chimeras in Gsalpha constructed from trisection of the sequence 125-213 of Gialpha2 were expressed stably, and clones were evaluated for the ability of the chimera to repress adipogenesis in response to the inducers, dexamethasone and methylisobutylxanthine, in combination. The chimera containing sequence 150-177 of Gialpha2 repressed adipogenesis, whereas the chimeras with either sequence 125-149 or 178-213 of Gialpha2 failed to repress induction of adipogenesis. Alanine-scanning mutagenesis of these two critical domains was performed first in clusters and then confirmed by analysis of single mutations. Six residues unique to Gsalpha were identified as critical to repression of adipogenesis, Asn167, Cys200, Leu203, Ser205, Val214, and Lys216. Leu203 and Ser205 are required in tandem, as mutagenesis to alanine of either one alone was without effect on repressor activity. The remaining four residues are required for repressor activity; mutation of any one of these abolishes the ability of Gsalpha to repress adipogenesis, although not affecting the ability of the mutant form of Gsalpha to regulate adenylylcyclase. Using conserved landmarks found in the crystal structures of Gialpha1 and Gsalpha, the Leu203 and Ser205 cluster appears to be exposed, closely aligned and located in switch I region. Asn167, Val214, and Lys216 project to regions on Gsalpha that are exposed in the GTPgammaS-liganded state of the alpha subunit. We speculate that these residues constitute an important contact domain between Gsalpha and the effector controlling adipogenesis, which is yet to be identified.

3T3 Cells↗
PubMed1998

The distribution of polycomb-group proteins during cell division and development in Drosophila embryos: impact on models for silencing.

The subcellular three-dimensional distribution of three polycomb-group (PcG) proteins-polycomb, polyhomeotic and posterior sex combs-in fixed whole-mount Drosophila embryos was analyzed by multicolor confocal fluorescence microscopy. All three proteins are localized in complex patterns of 100 or more loci throughout most of the interphase nuclear volume. The rather narrow distribution of the protein intensities in the vast majority of loci argues against a PcG-mediated sequestration of repressed target genes by aggregation into subnuclear domains. In contrast to the case for PEV repression (Csink, A.K., and S. Henikoff. 1996. Nature. 381:529-531), there is a lack of correlation between the occurrence of PcG proteins and high concentrations of DNA, demonstrating that the silenced genes are not targeted to heterochromatic regions within the nucleus. There is a clear distinction between sites of transcription in the nucleus and sites of PcG binding, supporting the assumption that most PcG binding loci are sites of repressive complexes. Although the PcG proteins maintain tissue-specific repression for up to 14 cell generations, the proteins studied here visibly dissociate from the chromatin during mitosis, and disperse into the cytoplasm in a differential manner. Quantitation of the fluorescence intensities in the whole mount embryos demonstrate that the dissociated proteins are present in the cytoplasm. We determined that <2% of PH remains attached to late metaphase and anaphase chromosomes. Each of the three proteins that were studied has a different rate and extent of dissociation at prophase and reassociation at telophase. These observations have important implications for models of the mechanism and maintenance of PcG- mediated gene repression.

Animals↗
PubMed1994

Physical and functional interactions between SH2 and SH3 domains of the Src family protein tyrosine kinase p59fyn.

The Src family protein tyrosine kinases participate in signalling through cell surface receptors that lack intrinsic tyrosine kinase domains. All nine members of this family possess adjacent Src homology (SH2 and SH3) domains, both of which are essential for repression of the enzymatic activity. The repression is mediated by binding between the SH2 domain and a C-terminal phosphotyrosine, and the SH3 domain is required for this interaction. However, the biochemical basis of functional SH2-SH3 interaction is unclear. Here, we demonstrate that when the SH2 and SH3 domains of p59fyn (Fyn) were present as adjacent domains in a single protein, binding of phosphotyrosyl peptides and proteins to the SH2 domain was enhanced, whereas binding of a subset of cellular polypeptide ligands to the SH3 domain was decreased. An interdomain communication was further revealed by occupancy with domain-specific peptide ligands: occupancy of the SH3 domain with a proline-rich peptide enhanced phosphotyrosine binding to the linked SH2 domain, and occupancy of the SH2 domain with phosphotyrosyl peptides enhanced binding of certain SH3-specific cellular polypeptides. Second, we demonstrate a direct binding between purified SH2 and SH3 domains of Fyn and Lck Src family kinases. Heterologous binding between SH2 and SH3 domains of closely related members of the Src family, namely, Fyn, Lck, and Src, was also observed. In contrast, Grb2, Crk, Abl, p85 phosphatidylinositol 3-kinase, and GTPase-activating protein SH2 domains showed lower or no binding to Fyn or Lck SH3 domains. SH2-SH3 binding did not require an intact phosphotyrosine binding pocket on the SH2 domain; however, perturbations of the SH2 domain induced by specific high-affinity phosphotyrosyl peptide binding abrogated binding of the SH3 domain. SH3-SH2 binding was observed in the presence of proline-rich peptides or when a point mutation (W119K) was introduced in the putative ligand-binding pouch of the Fyn SH3 domain, although these treatments completely abolished the binding to p85 phosphatidylinositol 3-kinase and other SH3-specific polypeptides. These biochemical SH2-SH3 interactions suggest novel mechanisms of regulating the enzymatic activity of Src kinases and their interactions with other proteins.

Amino Acid Sequence↗