Project description:The polymerase associated factor 1 complex (Paf1C) is a multifunctional epigenetic regulator of RNA polymerase II (Pol II) transcription. Paf1C controls gene expression by stimulating the placement of co-transcriptional histone modifications, influencing nucleosome occupancy in coding regions, facilitating transcription termination, and regulating nuclear export of RNAs. In this study, we investigate the extent to which these functions of Paf1C combine to influence the Saccharomyces cerevisiae transcriptome. Using conditions that enrich for unstable transcripts, we show that deletion of PAF1 affects all classes of Pol II-transcribed RNAs including multiple classes of noncoding transcripts. Gene ontology analysis revealed that mRNAs encoding genes involved in iron and phosphate homeostasis were differentially affected by deletion of PAF1. We further investigated these two groups of mRNAs with the goal of identifying overarching mechanisms of up and down-regulation in cells lacking Paf1. Our results indicate that only a subset of the observed changes result from loss of Paf1C-promoted histone modifications. We also found that transcription of the FET4 gene is differentially regulated by Paf1 and an upstream CUT. Together these data highlight the complexity of the epigenetic regulation of Pol II transcription imposed by Paf1C and identify a role for Paf1C in promoting CUT transcription.
Project description:H3 ChIP and input DNA were hybridized to Affymetrix GeneChip S. cerevisiae Tiling 1.0R Array Genome-wide mapping of nucleosomes generated by micrococcal nuclease (MNase) suggests that yeast promoter and terminator regions are very depleted of nucleosomes, predominantly because their DNA sequences intrinsically disfavor nucleosome formation. However, MNase has strong DNA sequence specificity that favors cleavage at promoters and terminators and accounts for some of the correlation between occupancy patterns of nucleosomes assembled in vivo and in vitro. Using an improved method for measuring nucleosome occupancy in vivo that does not involve MNase, we confirm that promoter regions are strongly depleted of nucleosomes, but find that terminator regions are much less depleted than expected. Unlike at promoter regions, nucleosome occupancy at terminators is strongly correlated with the orientation of and distance to adjacent genes. In addition, nucleosome occupancy at terminators is strongly affected by growth conditions, indicating that it is not primarily determined by intrinsic histone-DNA interactions. Rapid removal of RNA polymerase II (Pol II) causes increased nucleosome occupancy at terminators, strongly suggesting a transcription-based mechanism of nucleosome depletion. However, the distinct behavior of terminator regions and their corresponding coding regions suggests that nucleosome depletion at terminators is not simply associated with passage of Pol II, but rather involves a distinct mechanism linked to 3’ end formation.
Project description:We report change in the nucleosome occupancy and accessibility upon deletion of ATP-dependent chromatin remodellers (ISW1, ISW2 & CHD1) in Saccharomyces cerevisiae.
Project description:The Paf1 complex (Paf1C) is a conserved transcription elongation factor that regulates transcription elongation efficiency, facilitates co-transcriptional histone modifications, and impacts molecular processes linked to RNA synthesis, such as polyA site selection. Coupling of the activities of Paf1C to transcription elongation requires its association with RNA polymerase II (Pol II). Mutational studies in yeast identified Paf1C subunits Cdc73 and Rtf1 as important mediators of Paf1C association with Pol II on active genes. While the interaction between Rtf1 and the general elongation factor Spt5 is relatively well-understood, the interactions involving Cdc73 have not been fully elucidated. Using a site-specific protein cross-linking strategy in yeast cells, we identified direct interactions between Cdc73 and two components of the Pol II elongation complex, the elongation factor Spt6 and the largest subunit of Pol II. Both of these interactions require the tandem SH2 domain of Spt6. We also show that Cdc73 and Spt6 can interact in vitro and that rapid depletion of Spt6 dissociates Paf1 from chromatin, altering patterns of Paf1C-dependent histone modifications genome-wide. These results reveal interactions between Cdc73 and the Pol II elongation complex and identify Spt6 as a key factor contributing to the occupancy of Paf1C at active genes in Saccharomyces cerevisiae.
Project description:RSC (remodels the structure of chromatin) is an essential ATP-dependent chromatin remodeling complex in Saccharomyces cerevisiae. The catalytic subunit of RSC, Sth1 uses its ATPase activity to slide or remove nucleosomes. RSC has been shown to regulate the width of the nucleosome-depleted regions (NDRs) by sliding the flanking nucleosomes away from NDRs. As such the nucleosomes encroach NDRs when RSC is depleted and leads to transcription initiation defects. In this study, we examined the effects of the catalytic-dead Sth1 on transcription and compared them to the effects observed during acute and rapid Sth1 depletion by auxin-induced degron strategy. We found that rapid depletion of Sth1 reduces recruitment of TBP and Pol II in highly transcribed genes, as would be expected considering its role in regulating chromatin structure at promoters. In contrast, cells harboring the catalytic-dead Sth1 exhibited a severe reduction in TBP binding, but surprisingly, also displayed a substantial accumulation in Pol II occupancies within coding regions. After depleting endogenous Sth1 in the catalytic dead mutant, we observed a further increase in Pol II occupancies, suggesting that the inactive Sth1 contributed to the observed accumulation of Pol II in coding regions. Notwithstanding the Pol II increase, the ORF occupancies of histone chaperones FACT and Spt6 were significantly reduced in the mutant. These results suggest a potential role for RSC in recruiting/retaining these chaperones in coding regions. Pol II accumulation despite substantial reductions in TBP, FACT, and Spt6 occupancies in the catalytic-dead mutant could be indicative of severe transcription elongation and termination defects. Such defects would be consistent with studies showing that RSC is recruited to coding regions in a transcription-dependent manner. Thus, these findings imply a role for RSC in transcription elongation and termination processes, in addition to its established role in transcription initiation.
Project description:Nuclear depletion of the essential transcription termination factor Nrd1 in Saccharomyces cerevisiae was studied using a combination of RNA-Seq, ChIP-Seq of Pol II and PAR-CLIP of Nrd1. The drug rapamycin induces the formation of a ternary complex between a protein of interest, the drug and the small subunit of the ribosome (both proteins are genetically engineered). The small ribosome subunit is transported out of the nucleus. therefore the protein of interest can be depleted from nucleus upon treatment with rapamycin.
Project description:Transcription of mRNA products by RNA polymerase II (Pol II) is a multi-stage event subject to a multitude of regulatory processes. Transcription, RNA processing, and chromatin related factors all interact with Pol II to ensure proper timing and coordination of transcription and co-transcriptional processes. Many regulators must function simultaneously to coordinate these processes, yet few strategies exist to explore the full complement of factors regulating specific stages of transcription. To this end we developed a strategy to purify Pol II elongation complexes from specific loci of a single gene, namely the 5′ and 3′ regions, using sequences in the nascent RNA. Applying this strategy to Saccharomyces cerevisiae we determined the specific set of factors that interact with Pol II at precise stages during transcription. We identify many known region-specific factors as well as determine a role for the transcription termination factor Rai1 in regulating the early stages of transcription genome-wide. We also demonstrate a role for the ubiquitin ligase Bre1 in regulating Pol II dynamics during the latter stages of transcription. This strategy for gene and loci-specific isolation of transcription complexes will provide a useful tool to explore the host of factors that regulate the different stages of transcription and coordinate co-transcriptional processes.
Project description:Saccharomyces cerevisiae is an excellent microorganism for industrial succinic acid production, but high succinic acid concentration will inhibit the growth of Saccharomyces cerevisiae then reduce the production of succinic acid. Through analysis the transcriptomic data of Saccharomyces cerevisiae with different genetic backgrounds under different succinic acid stress, we hope to find the response mechanism of Saccharomyces cerevisiae to succinic acid.