Project description:Genomic features of DSB re-landscaping in rtf1 mutants. Histone modification is a critical determinant of frequency and location of double-strand breaks (DSBs), which induce recombination during meiosis. The Set1-dependent histone H3K4 and Dot1-dependent H3K79 methylations play an important role in DSB formations in budding yeast. Both methylations are promoted by the RNA polymerase II associated factor 1 (Paf1) complex, Paf1C. This study addressed a role of the Paf1C component Rtf1, which is critical for H3K4 and H3K79 methylations, for the regulation of meiotic DSB formation. Similar to set1 mutation, rtf1 mutation decreased the occurrence of DSBs in the genome. The rtf1 set1 double mutant exhibited a larger reduction in the levels of DSBs than the frequency of DSBs detected in either of the single mutants; this indicates independent roles of Rtf1 and Set1 in DSB formation. Importantly, the distribution of DSBs along chromosomes in the rtf1 mutant changed in a different manner than the pattern observed in the set1 and set1 dot1 mutants; this was characterized by enhanced DSB formation at some DSB-cold regions. These observations suggest that Rtf1, and, possibly, the Paf1C, determine DSB landscape in the genome, independent of H3K4 methylation.
Project description:This study has determined structure of transcription initiation complexes including a DNA-bound activator, RNA polymerase II (Pol II), and Mediator on a divergent promoter GAL80/SUT719 using a combination of cryo-EM and XL-MS analyses. Our cryo-EM single-particle analysis reveals a dimeric form of Med-PIC through the Mediator Tail module induced by the activator protein. Density of the upstream DNA bound to the Gal4-VP16 was identifiable along the Mediator Tail module, while XL-MS localized flexible regions that were not visible by cryo-EM analysis, such as activator-binding domains (ABDs and KIX).
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:In cells lacking the histone methyltransferase Set2, initiation of RNA polymerase II transcription occurs inappropriately within the protein-coding regions of genes, rather than being restricted to the proximal promoter. Here, we mapped the transcripts produced in an S. cerevisiae strain lacking Set2, and applied rigorous statistical methods to identify sites of cryptic transcription at high resolution.