Increase in chromatin accessibility to MNase at sites of DNA replication
Ontology highlight
ABSTRACT:
ORGANISM(S): Saccharomyces cerevisiae
PROVIDER: GSE43548 | GEO | 2013/01/17
SECONDARY ACCESSION(S): PRJNA186689
REPOSITORIES: GEO
Similar Datasets
Project description:Faithful DNA replication is essential for normal cell division and differentiation. In eukaryotic cells, DNA replication takes place on chromatin. This poses the critical question as to how DNA replication can progress through chromatin, which is inhibitory to all DNA-dependent processes. Here, we have developed a novel genome-wide method to measure chromatin accessibility to micrococcal nuclease that is normalized for nucleosome density, NCAM (Normalized Chromatin Accessibility to MNase) assay. This method enabled us to discover that chromatin accessibility increases specifically at and ahead of DNA replication forks in normal S phase and during replication stress. We further found that Mec1, a key regulatory ATR-like kinase in the S-phase checkpoint, is required for both normal chromatin accessibility around replication forks and replication fork rate during replication stress. In this study we sought to analyze the chromatin structural changes that take place at sites of DNA replication. To this end, we obtained yeast cell populations synchronously undergoing DNA replication by M-NM-1-factor G1 arrest and release. In order to analyze chromatin structure at sites of DNA replication we first mapped the genomic locations undergoing DNA replication to high-resolution, strand-specific microarrays tiling chromosomes III, VI, and XII, covering ~14% of the genome. Two complementary approaches were taken: (1) we mapped fork positions by chromatin immunoprecipitation (ChIP) of a FLAG-tagged DNA polymerase 1 (Pol1), a replication fork component and (2) we mapped the sites of active DNA synthesis by generating DNA copy number profiles. We then analyzed chromatin structure at the sites of DNA replication by Micrococcal nuclease mononucleosome mapping and by generating histone H3 density maps. We further generated a Normalized Chromatin Accessibility to MNase (NCAM) signal by normalizing MNase mononucleosome signal for histone H3 density. NCAM signal represents a measure of nucleosome accessibility to MNase that is normalized for nucleosome content. These three approaches allowed us to assess potential changes in nucleosome positioning, nucleosome density, and nucleosome accessibility during DNA replication. We searched for changes in chromatin structure by comparing, during S phase, regions undergoing DNA replication to those not yet replicated, and also by comparing the same region before replication (not replicated, G1 arrested control) and during DNA replication in S phase. We typically harvested S phase cells at 30 or 60 minutes after release from G1 arrest. Experimental conditions included releasing cells into rich media at 24M-BM-0C or into rich media containing 200 mM Hydroxyurea (HU). Both conditions slowed down replication fork rate and made these experiments feasible. For each strain, samples for the different experiments (Chromatin for Pol1 and H3 ChIP, in vivo MNase digestion, and DNA for DNA copy number profiles) were harvested simultaneously for each time point. Therefore, comparisons between time points for each strain must be made using samples from the same replicate experiment. Our analysis included WT cells, as well as S phase checkpoint mutants (M-NM-^Tmec1 M-NM-^Tsml1 and mec1-100 M-NM-^Tsml1), as well as control strains (M-NM-^Tsml1).
2013-01-17 | E-GEOD-43548 | biostudies-arrayexpress
Project description:The Mec1 and Rad53 kinases play a central role during acute replication stress in budding yeast. They are also essential for viability in normal growth conditions, but the signal that activates the Mec1–Rad53 pathway in the absence of exogenous insults is currently unknown. Here, we show that this pathway is active at the onset of normal S phase because dNTP levels present in G1 phase are not sufficient to support processive DNA synthesis and impede DNA replication. This activation can be suppressed experimentally by increasing dNTP levels in G1 phase. Moreover, we show that unchallenged cells entering S phase in the absence of Rad53 undergo irreversible fork collapse and mitotic catastrophe. Together, these data indicate that cells use dNTP shortage to detect the onset of DNA replication and activate the Mec1–Rad53 pathway, which in turn maintains functional forks and triggers dNTP synthesis, allowing the completion of DNA replication.
2020-03-17 | GSE136601 | GEO
Project description:The Mec1 and Rad53 kinases play a central role during acute replication stress in budding yeast. They are also essential for viability in normal growth conditions, but the signal that activates the Mec1–Rad53 pathway in the absence of exogenous insults is currently unknown. Here, we show that this pathway is active at the onset of normal S phase because dNTP levels present in G1 phase are not sufficient to support processive DNA synthesis and impede DNA replication. This activation can be suppressed experimentally by increasing dNTP levels in G1 phase. Moreover, we show that unchallenged cells entering S phase in the absence of Rad53 undergo irreversible fork collapse and mitotic catastrophe. Together, these data indicate that cells use dNTP shortage to detect the onset of DNA replication and activate the Mec1–Rad53 pathway, which in turn maintains functional forks and triggers dNTP synthesis, allowing the completion of DNA replication.
2020-03-17 | GSE136602 | GEO
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs. We queried the yeast genome for DSBs after cells were treated with 200 mM hydroxyurea during S phase. Samples were collected from 1) cells synchronized in G1 phase by alpha factor; 2) cells released from G1 into medium containing 200 mM hydroxyurea for 1 h; 3) cells recovering in fresh medium without hydroxyurea for 1 h after the 1 h exposure to HU. These samples are referred to as G1, HU 1h, and R 1h, respectively. The strains from which the samples were collected are indicated following the time point, e.g. G1_MEC1 or R 1h_mec1. The experiment with mec1 was done twice (Experiments A and B) and that with MEC1 was done once (Experiment C). In addition, a control experiment of in vitro digestion with BamHI using the G1_mec1 sample (G1_BamHI) was performed.
2015-01-12 | E-GEOD-58808 | biostudies-arrayexpress
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs. We queried the yeast genome for gene expression after cells were treated with 200 mM hydroxyurea during S phase. Samples were collected from 1) cells synchronized in G1 phase by alpha factor; 2) cells released from G1 into medium containing 200 mM hydroxyurea for 1 h; 3) cells recovering in fresh medium without hydroxyurea for 30 and 60 min after the 1 h exposure to HU. These samples are referred to as G1, HU 1h, R30, and R60, respectively. The strains from which the samples were collected are indicated before the time point, e.g. mec1_G1 or MEC1_R30. Stranded mRNA libraries were prepared according to manufacturer's suggestion and sequenced on Illumina MiSeq with paired-end reads of 75 bp.
2015-01-12 | E-GEOD-63516 | biostudies-arrayexpress
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs.
2015-01-12 | GSE63516 | GEO
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs.
2015-01-12 | GSE58808 | GEO
Project description:The cohesin complex holds together newly-replicated chromatids and is involved in diverse pathways that preserve genome integrity. We show that in budding yeast, cohesin is transiently recruited to active replication origins and it spreads along DNA as forks progress. When DNA synthesis is impeded, cohesin accumulates at replication sites and is critical for the recovery of stalled forks. Cohesin enrichment at replication forks does not depend on H2A(X) formation, which differs from its loading requirements at DNA double-strand breaks (DSBs). However, cohesin localization is largely reduced in rad50delta mutants and cells lacking both Mec1 and Tel1 checkpoint kinases. Interestingly, cohesin loading at replication sites depends on the structural features of Rad50 that are important for bridging sister chromatids, including the CXXC hook domain and the length of the coiled-coil extensions. Together, these data reveal a novel function for cohesin in the maintenance of genome integrity during S phase. Scc1 ChIP, Rad50 ChIP and BrdU IP in wild type and mutants at different stages of the cell cycle.
2012-10-01 | E-GEOD-39078 | biostudies-arrayexpress
Project description:The cohesin complex holds together newly-replicated chromatids and is involved in diverse pathways that preserve genome integrity. We show that in budding yeast, cohesin is transiently recruited to active replication origins and it spreads along DNA as forks progress. When DNA synthesis is impeded, cohesin accumulates at replication sites and is critical for the recovery of stalled forks. Cohesin enrichment at replication forks does not depend on H2A(X) formation, which differs from its loading requirements at DNA double-strand breaks (DSBs). However, cohesin localization is largely reduced in rad50delta mutants and cells lacking both Mec1 and Tel1 checkpoint kinases. Interestingly, cohesin loading at replication sites depends on the structural features of Rad50 that are important for bridging sister chromatids, including the CXXC hook domain and the length of the coiled-coil extensions. Together, these data reveal a novel function for cohesin in the maintenance of genome integrity during S phase.
2012-10-01 | GSE39078 | GEO
Project description:Hundreds of DNA replication forks functioning simultaneously are essential for timely DNA duplication, but the organization of replication forks are poorly understood in mammalian cells. Here, we developed a replication-enriched in situ HiC (Repli-HiC) method to capture chromatin contacts located adjacent to replication forks and found two types of fountain-like chromatin contacts at thousands of loci. Interactions within fountain-spanning regions are confirmed by q3C-seq analysis of different stages of S phase cells.
2024-03-04 | GSE230613 | GEO