Project description:Transcription factors (TFs) play a central role in regulating gene expression by interacting with cis regulatory DNA elements associated with their target genes. Recent surveys have examined the DNA binding specificities of most Saccharomyces cerevisiae transcription factors but a comprehensive evaluation of their data has been lacking. Results: We analyzed in vitro and in vivo TF-DNA binding data reported in previous large-scale studies to generate a comprehensive, curated resource of DNA binding specificity data for all characterized S. cerevisiae transcription factors. Our collection comprises DNA binding site motifs and comprehensive in vitro DNA binding specificity data for all possible 8 bp sequences. Included in this database is DNA binding specificity data for 27 TFs independently generated by PBM analysis in this current study. Investigation of the DNA binding specificities within the basic leucine zipper (bZIP) and VHR transcription factor families revealed unexpected plasticity in TF-DNA recognition: intriguingly, the VHR transcription factors, newly characterized by protein binding microarrays in this study, recognize bZIP like DNA motifs, while the bZIP transcription factor Hac1 recognizes a motif highly similar to the canonical E-box motif of basic helix-loop-helix (bHLH) transcription factors. We identified several transcription factors with distinct primary and secondary motifs, which might be associated with different regulatory functions. Finally, integrated analysis of in vivo transcription factor binding data with protein binding microarray data lends further support for indirect DNA binding in vivo by sequence-specific transcription factors.
Project description:Transcription factors (TFs) play a central role in regulating gene expression by interacting with cis regulatory DNA elements associated with their target genes. Recent surveys have examined the DNA binding specificities of most Saccharomyces cerevisiae transcription factors but a comprehensive evaluation of their data has been lacking. Results: We analyzed in vitro and in vivo TF-DNA binding data reported in previous large-scale studies to generate a comprehensive, curated resource of DNA binding specificity data for all characterized S. cerevisiae transcription factors. Our collection comprises DNA binding site motifs and comprehensive in vitro DNA binding specificity data for all possible 8 bp sequences. Included in this database is DNA binding specificity data for 27 TFs independently generated by PBM analysis in this current study. Investigation of the DNA binding specificities within the basic leucine zipper (bZIP) and VHR transcription factor families revealed unexpected plasticity in TF-DNA recognition: intriguingly, the VHR transcription factors, newly characterized by protein binding microarrays in this study, recognize bZIP like DNA motifs, while the bZIP transcription factor Hac1 recognizes a motif highly similar to the canonical E-box motif of basic helix-loop-helix (bHLH) transcription factors. We identified several transcription factors with distinct primary and secondary motifs, which might be associated with different regulatory functions. Finally, integrated analysis of in vivo transcription factor binding data with protein binding microarray data lends further support for indirect DNA binding in vivo by sequence-specific transcription factors. 27 Protein binding microarray (PBM) experiments of Saccharomyces cerevisiae transcription factors were performed. Briefly, the PBMs involved binding GST-tagged yeast transcription factors to double-stranded 44K Agilent microarrays in order to determine their sequence preferences. The method is described in Berger et al., Nature Biotechnology 2006 (PMID 16998473). A key feature is that the microarrays are composed of de Bruijn sequences that contain each 10-base sequence once and only once, providing an evenly balanced sequence distribution. Individual de Bruijn sequences have different properties, including representation of gapped patterns. The array probe sequences on the custom array design used in this study were reported previously in Berger et al., Cell 2008 (PMID 18585359) and are available via an academic research use license. Here we provide the data transformed into median signal intensities (after normalization and detrending of the original array data) for all 32,896 8-base sequences, Z-scores for these intensities, and E-scores. E-scores are a modified version of AUC and describe how well each 8-mer ranks the intensities of the spots. In general, the E-scores are slightly more reproducible than Z-scores, but contain less information about relative binding affinity. Additional experimental details are found in Berger et al., Nature Biotechnology 2006, Gordan et al., Genome Biology (in press), and the accompanying Supplementary information.
Project description:Binding of transcription factors to DNA is a key regulatory step in the control of gene expression. DNA sequences with high affinity for transcription factors occur more frequently in the genome than instances of genes bound or regulated by these factors. Although several mechanisms have been identified that influence the specificity of transcriptional regulation, it is not known if these can explain the observed genome-wide pattern of binding or regulation for a given transcription factor. We used genome-wide approaches to study how trans influences shape the binding and regulatory landscape of Pho4, a budding yeast transcription factor that activates gene expression in response to phosphate limitation. We find that nucleosomes significantly restrict the sites to which Pho4 binds. At nucleosome-depleted sites, competition between Pho4 and another transcription factor, Cbf1, determines Pho4 occupancy, raising the threshold for transcriptional activation by Pho4 in phosphate replete conditions and preventing Pho4 activation of genes outside the phosphate regulon during phosphate starvation. Pho4 binding is not sufficient for transcriptional activation - a cooperative interaction between the transcription factor Pho2 and Pho4 occurs specifically at genes that are activated. Combining these experimental observations, we are able to globally predict Pho4 binding and its functionality. Our study provides insights into the mechanisms of global control by sequence-specific transcription factors. ChIP-Seq experiments of Pho4, Pho2 and Cbf1 samples and paired-end nucleosome sequencing in no Pi conditions.
Project description:The tumor suppressor PP2A is a major cellular protein phosphatase that regulates numerous cellular processes through the formation of holoenzymes containing distinct regulatory B-subunits. However, the determinants of differential substrate dephosphorylation by PP2A are poorly understood. Here, we develop a specific genetically encoded inhibitor of PP2A-B56 and perform global phosphoproteomic studies to identify hundreds of regulated phosphorylation sites. We show that PP2A-B56 substrate specificity is controlled by affinity and position of B56 binding motifs and that PP2A active site preference is determined by the B-subunit. These insights uncover PP2A-B56 as a novel negative regulator of ADAM17 mediated growth factor signalling and tumor development. Collectively our work identifies basic principles of PP2A-B56 specificity with broad implications for understanding signalling in eukaryotes.
Project description:The sequence specificity of DNA-binding proteins is the primary mechanism by which the cell recognizes genomic features. Here, we describe systematic determination of yeast transcription factor DNA-binding specificities. We obtained binding specificities for 112 DNA-binding proteins representing 19 distinct structural classes. One-third of the binding specificities have not been previously reported. Several binding sequences have striking genomic distributions relative to transcription start sites, supporting their biological relevance and suggesting a role in promoter architecture. Among these are Rsc3 binding sequences, containing the core CGCG, which are found preferentially ~100 bp upstream of transcription start sites. Mutation of RSC3 results in a dramatic increase in nucleosome occupancy in hundreds of proximal promoters containing a Rsc3 binding element, but has little impact on promoters lacking Rsc3 binding sequences, indicating that Rsc3 plays a broad role in targeting nucleosome exclusion at yeast promoters. Keywords: Protein binding microarrays, DNA, proteins
Project description:Homeodomains (HDs) are the second largest class of DNA binding domains (DBDs) in eukaryotic sequence-specific transcription factors (TFs) and are the TF structural class with the largest number of disease mutations in the Human Gene Mutation Database (HGMD). Despite numerous structural studies and large-scale analyses of HD DNA binding specificity, HD-DNA recognition is still not fully understood. Here, we analyzed 92 human HD mutants, including disease-associated variants and variants of unknown significance (VUS), for their effects on DNA binding activity. Many of the variants altered DNA binding affinity and/or specificity. Structural analysis identified 14 novel specificity-determining positions, 5 of which do not contact DNA. The same missense substitution at analogous positions within different HDs exhibited different effects on DNA binding activity. Variant effect prediction tools perform moderately well in distinguishing variants with altered DNA binding affinity, but poorly in identifying those with altered binding specificity. Our results highlight the need for biochemical assays of TF coding variants and promote dozens of variants for further investigations into their pathogenicity and the development of clinical diagnostics and precision therapies.
Project description:Binding of transcription factors to DNA is a key regulatory step in the control of gene expression. DNA sequences with high affinity for transcription factors occur more frequently in the genome than instances of genes bound or regulated by these factors. Although several mechanisms have been identified that influence the specificity of transcriptional regulation, it is not known if these can explain the observed genome-wide pattern of binding or regulation for a given transcription factor. We used genome-wide approaches to study how trans influences shape the binding and regulatory landscape of Pho4, a budding yeast transcription factor that activates gene expression in response to phosphate limitation. We find that nucleosomes significantly restrict the sites to which Pho4 binds. At nucleosome-depleted sites, competition between Pho4 and another transcription factor, Cbf1, determines Pho4 occupancy, raising the threshold for transcriptional activation by Pho4 in phosphate replete conditions and preventing Pho4 activation of genes outside the phosphate regulon during phosphate starvation. Pho4 binding is not sufficient for transcriptional activation - a cooperative interaction between the transcription factor Pho2 and Pho4 occurs specifically at genes that are activated. Combining these experimental observations, we are able to globally predict Pho4 binding and its functionality. Our study provides insights into the mechanisms of global control by sequence-specific transcription factors.
Project description:MHC class II (MHCII) genes are transactivated by the NOD-like receptor (NLR) factor CIITA, which is recruited to SXY regulatory modules of MHC promoters via a DNA-binding “enhanceosome” complex. NLRC5, another NLR protein, was recently found to control transcription of MHC class I (MHCI) genes. However, detailed understanding of its target-gene specificity and mechanism of action remained lacking. We therefore performed ChIP-sequencing experiments to gain comprehensive information on NLRC5-transactivated genes. In addition to classical MHCI genes, we identified novel NLRC5-targets exclusively in the H2-Q and H2-T regions of the MHCI locus, among which the best targets were found. Investigation of cells lacking the MHCII-enhanceosome factor RFX5 demonstrated its strict requirement for NLRC5 recruitment to the SXY module conserved in MHCI genes. Furthermore, patient-derived B cell lines deficient in RFX5, RFXAP, and RFXANK corroborated importance of the enhanceosome for MHCI transactivation. Although sharing similar SXY modules and common DNA-binding factors, CIITA and NLRC5 regulate distinct genes, as shown here using double-deficient Nlrc5-/-CIIta-/- mice. The identification of sequences occupied by NLRC5 in vivo allowed us to define a unique consensus motif for its recruitment, which diverges from that used by CIITA. Our results thus broaden our knowledge on transcriptional activity of NLRC5, highlighting its remarkable selectivity for genes encoding MHCI or related proteins and providing insights into the specificity of its recruitment. Analysis of Nlrc5 binding sites in T-cells
Project description:Yeast knockout collection TAG microarrays are an emergent platform for rapid, genome-wide functional characterization of yeast genes. We describe a method for analyzing two-color array data to efficiently represent differential knockout strain representation across two experimental conditions. Using a fully defined spike-in pool, we show that the sensitivity and specificity of this method exceed typical current approaches. Keywords: Saccharomyces cerevisiae, yeast, self_vs_self, spike-in pools