Unknown,Transcriptomics,Genomics,Proteomics

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High throughput sequencing enables detailed analysis of S. cerevisiae DNA replication

ABSTRACT: We have used three complementary deep sequencing approaches to characterise the temporal order of genome replication in S. cerevisiae. Each approach measures the increase in DNA copy number as a genomic region is replicated (in a large population of cells). We find that the use of deep sequencing provided high spatial resolution. For maximum temporal resolution we have measured replication dynamics at multiple time points during a synchronous S phase. To pinpoint replication origins we have synchronously released a checkpoint mutant (rad53-delta) into S phase under conditions of depleted dNTPs (200 mM hydroxyurea; HU) and measured the increase in DNA copy number after 60 minutes. Finally for rapid characterisation of replication dynamics in wild-type cells from an unperturbed cell cycle we have obtained replicating (S phase) and non-replicating (G2 phase) cells by fluorescence activated cell sorting (FACS) and subjected the DNA to copy number analysis. We have compared and contrasted these approaches and developed the tools required for interpreting the deep sequencing data. Measurement of genome replication time for various S. cerevisiae strains. For each strain two samples were analysed: a replicating sample (from S phase) and a non-replicating sample (from G2 phase).

ORGANISM(S): Saccharomyces cerevisiae

SUBMITTER: Conrad Nieduszynski

PROVIDER: E-GEOD-48212 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Eukaryotic DNA replication initiates from multiple sites on each chromosome called replication origins. In the budding yeast Saccharomyces cerevisiae, origins are defined at discrete sites. Regular spacing and diverse firing characteristics of origins are thought to be required for efficient completion of replication, especially in the presence of replication stress. However, a S. cerevisiae chromosome III harboring multiple origin deletions has been reported to replicate relatively normally, and yet how an origin-deficient chromosome could accomplish successful replication remains unkown. To address this issue, we deleted seven well-characterized origins from chromosome VI, and found that thsese deletions do not cause gross growth defects even in the presence of replication inhibitors. We demonstrated that the origin deletions do cause a strong decrease in the binding of the origin recognition complex. Unexpectedly, replication profiling of this chromosome showed that DNA replication initiates from non-canonical loci around deleted origins in yeast. These results suggest that replication initiation can be unexpectedly flexible in this organism. In this study, we aimed to establish an independent system to investigate how an origin-deficient chromosome is replicated. To this end, we systematically deleted seven well-characterized origins on the left arm of S. cerevisiae chromosome VI and analyzed (1) Orc2 localization during G2/M arrest and (2) BrdU incorporation during synchronous release from G1 arrest into S-phase, and compared the results to wild-type cell signals. For Orc2 ChIP-Chip experiments, Orc-bound DNA was isolated from Orc2-2Xlinker-3XFlag epitope-tagged cells arrested in G2/M using antibodies against Flag. For BrdU ChIP-Chip experiments, actively replicating DNA was isolated from cells harboring a single integrated BrdU incorporation vector released synchronously into 200mM HU using antibodies against BrdU. Immunoprecipitated and input (Orc2) or G1 (BrdU) DNA was then amplified and competitively hybridized to high-resolution strand-specific microarrays covering chromosomes III, VI, and XII.

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High throughput sequencing enables detailed analysis of S. cerevisiae DNA replication

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