Project description:Background: Chromatin remodeling complexes facilitate the access of enzymes that mediate transcription, replication or repair of DNA by modulating nucleosome position and/or composition. Ino80 is the DNA-dependent Snf2-like ATPase subunit of a complex whose nucleosome remodeling activity requires actin-related proteins, Arp4, Arp5 and Arp8, as well as two RuvB-like DNA helicase subunits. Budding yeast mutants deficient for Ino80 function are not only hypersensitive to reagents that induce DNA double strand breaks, but also to those that impair replication fork progression. Results: To understand why ino80 mutants are sensitive to agents that perturb DNA replication, we used chromatin immunoprecipitation to map the binding sites of the Ino80 chromatin remodeling complex on four budding yeast chromosomes. We found that Ino80 and Arp5 binding sites coincide with origins of DNA replication and tRNA genes. In addition, Ino80 was bound at 67% of the promoters of genes that are sensitive to ino80 mutation. When replication forks were arrested near origins in the presence of hydroxyurea (HU), the presence of the Ino80 complex at stalled forks and at unfired origins increased dramatically. Importantly, the resumption of DNA replication after release from a HU block was impaired in the absence of Ino80 activity. Mutant cells accumulated double-strand breaks as they attempted to restart replication. Consistently, ino80-deficient cells, although proficient for checkpoint activation, delay recovery from the checkpoint response. Conclusions: The Ino80 chromatin remodeling complex is enriched at stalled replication forks where it promotes the resumption of replication upon recovery from fork arrest. Keywords: ChIP-chip
Project description:The carboxy-terminal domain (CTD) of Rpb1, the largest component of the 12-subunit RNA polymerase II, consists of repeating Y1S2P3T4S5P6S7 heptapeptides (26 repeats in budding yeast). Each stage of transcription relies on the ordered recruitment and exchange of specific protein complexes that act on RNA polymerase II, its nascent transcripts, and the underlying chromatin. This dynamic process is orchestrated via patterned post-translational modifications of the CTD. To characterize the role of phosphorylation on Thr4, we examined the effect of Rpb1 alleles in which Thr4 was substituted with an alanine (T4A) or the phospho-mimic glutamate (T4E). Substitutions were made across all heptad repeats of the CTD.
We affinity purified HA-tagged Rpb1 from Saccharomyces cerevisiae strains bearing WT, T4A, and T4E CTDs. A control strain (Z26) lacking the HA-tagged Rpb1 was subjected to an identical affinity enrichment procedure. Three biological replicates were acquired for each type of affinity purification and analyzed independently. After TCA-precipitation, proteins were urea-denatured, reduced, alkylated, then digested with endoproteinase LysC followed by trypsin. The resulting peptide mixtures were analyzed by Multidimensional Protein Identification Technology (MudPIT). Label-free quantitative proteomics was used to identify and quantify the relative abundance of affinity-enriched complexes.
Project description:Background: Chromatin remodeling complexes facilitate the access of enzymes that mediate transcription, replication or repair of DNA by modulating nucleosome position and/or composition. Ino80 is the DNA-dependent Snf2-like ATPase subunit of a complex whose nucleosome remodeling activity requires actin-related proteins, Arp4, Arp5 and Arp8, as well as two RuvB-like DNA helicase subunits. Budding yeast mutants deficient for Ino80 function are not only hypersensitive to reagents that induce DNA double strand breaks, but also to those that impair replication fork progression. Results: To understand why ino80 mutants are sensitive to agents that perturb DNA replication, we used chromatin immunoprecipitation to map the binding sites of the Ino80 chromatin remodeling complex on four budding yeast chromosomes. We found that Ino80 and Arp5 binding sites coincide with origins of DNA replication and tRNA genes. In addition, Ino80 was bound at 67% of the promoters of genes that are sensitive to ino80 mutation. When replication forks were arrested near origins in the presence of hydroxyurea (HU), the presence of the Ino80 complex at stalled forks and at unfired origins increased dramatically. Importantly, the resumption of DNA replication after release from a HU block was impaired in the absence of Ino80 activity. Mutant cells accumulated double-strand breaks as they attempted to restart replication. Consistently, ino80-deficient cells, although proficient for checkpoint activation, delay recovery from the checkpoint response. Conclusions: The Ino80 chromatin remodeling complex is enriched at stalled replication forks where it promotes the resumption of replication upon recovery from fork arrest. Keywords: ChIP-chip