Project description:Phosphorylation of histone H2AX is an early response to DNA damage in eukaryotes. In Saccharomyces cerevisiae, DNA damage or replication fork stalling results in histone H2A phosphorylation to yield gamma-H2A (yeast gamma-H2AX) in a Mec1 (ATR)- and Tel1 (ATM)- dependent manner. Here, we describe the genome-wide location analysis of gamma-H2A as a strategy to identify loci prone to engage the Mec1 and Tel1 pathways. Remarkably, gamma-H2A enrichment overlaps with loci prone to replication fork stalling and is caused by the action of Mec1 and Tel1, indicating that these loci are prone to breakage. Moreover, about half the sites enriched for gamma-H2A map to repressed protein-coding genes, and histone deacetylases are necessary for formation of gamma-H2A at these loci. Finally, our work indicates that high resolution mapping of gamma-H2AX is a fruitful route to map fragile sites in eukaryotic genomes.
Project description:DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins RPA, SMC5, gamma-H2AX, and BRCA1 in B cells subjected to replication stress. Protein-DNA association for four DNA damage response proteins (RPA, SMC5, g-H2AX, BRCA1), BrdU incorporation, and gene transcription in B lymphocytes with and without hydroxyurea treatment were examined.
Project description:Phosphorylation of the histone variant H2AX forms γ-H2AX that marks DNA double-strand break (DSB). Here we generated the sequencing-based maps of H2AX and γ-H2AX positioning in resting and proliferating cells before and after ionizing irradiation. Genome-wide locations of possible endogenous and exogenous DSBs were identified based on γ-H2AX distribution in dividing cancer cells without irradiation and that in resting cells upon irradiation, respectively. γ-H2AX-enriched regions of endogenous origin in replicating cells included telomeres and active transcription start sites, apparently reflecting replication- and transcription-mediated stress during rapid cell division. Surprisingly, H2AX itself, prior to phosphorylation, was specifically located at these endogenous hotspots. This phenomenon was only observed in dividing cancer cells but not in resting cells. Endogenous H2AX was concentrated on the transcription start site of actively transcribed genes but was irrelevant to pausing of RNA polymerase II (pol II), which precisely coincided with γ-H2AX of endogenous origin. γ-H2AX enrichment upon irradiation also coincided with actively transcribed regions, but unlike endogenous γ-H2AX, it extended into the gene body and was not specifically concentrated on the pausing site of pol II. Subtelomeres were not responsive to external DNA damage. Our findings provide insight into DNA repair programs of cancer and may have implications for cancer therapy.
Project description:DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins DNA double strand breaks (DSBs) in B lymphocytes are thought to arise stochastically during replication (S phase) or as a result of targeted DNA damage by activation induced cytidine deaminase (AID) in G1. Here we identify a novel class of recurrent, early replicating and AID independent DNA lesions, termed early replication fragile sites (ERFS), by genome-wide localization of DNA repair proteins RPA, SMC5, gamma-H2AX, and BRCA1 in B cells subjected to replication stress.
Project description:Phosphorylation of the histone variant H2AX forms γ-H2AX, which serves as a marker of DNA repair response. Here we provide ChIP-seq-based maps of histone H2AX, γ-H2AX, H2AZ, INO80, SRCAP, and RNA polymerase II in activated T cells. Matched data for H2AX and γ-H2AX in resting T cells and Jurkat cancer T cells are available in GSE25577.
Project description:The structural complexity of nucleosomes underlies their functional versatility. Here we report a new type of complexity – nucleosome fragility, manifested as high sensitivity to micrococcal nuclease, in contrast to the common presumption that nucleosomes are similar in resistance to MNase digestion. Using differential MNase digestion of chromatin and high-throughput sequencing, we have identified a special group of nucleosomes termed fragile nucleosomes throughout the yeast genome, nearly one thousand of which are at previously determined “nucleosome free” loci. Nucleosome fragility is broadly implicated in multiple chromatin processes, including transcription, translocation and replication, in correspondence to specific physiological states of cells. In the environmental-stress-response genes, the presence of fragile nucleosomes prior to the occurrence of environmental changes suggests that nucleosome fragility poises genes for swift up-regulation in response to the environmental changes. We propose that nucleosome fragility underscores distinct functional statuses of the chromatin and provides a new dimension for portraying the landscape of genome organization.