Project description:The budding yeast genome is marked by 250-350 origins of DNA replication. These origins are bound by the origin recognition complex (ORC) throughout the cell cycle. ORC has known DNA binding sequence preferences which, though necessary for binding, are not sufficient to fully specify a genomic locus as being bound by ORC, indicating that the cell must use additional chromosomal cues to specify ORC binding sites and origins of replication. Using high-throughput sequencing to precisely locate both ORC binding sites and nucleosome locations genome-wide, we find that a nucleosome depleted region (NDR) and precisely positioned nucleosomes are a ubiquitous feature of yeast replication origins. The ARS consensus sequence (ACS) and adjacent sequences are sufficient to maintain the nucleosome-free properties of the NDR. We use a temperature sensitive ORC1 mutant to demonstrate that ORC is required to maintain precisely positioned nucleosomes at origins of replication. These findings demonstrate the importance of local nucleosome positioning at replication origins, and that chromatin organization is an important determinant of origin selection. Examination of nucleosome positioning in wild-type and orc1-161ts mutant S. cerevisiae at room temperature and heatshock temperatures. Examination of ORC binding locations by ChIP-seq. All reported coordinates are based on the SGD genome build released 12/16/2005.
Project description:Background: The replication program of vertebrate genomes is driven by the chromosomal distribution and timing of activation of ten of thousands replication origins. Genome-wide studies have shown the frequent association of origins with promoters and CpG islands, and their enrichment in G-quadruplexes sequence motifs (G4). However the genetic determinants driving their activity remain poorly understood. To gain insight on functional constraints operating on replication origins and on their spatial distribution, we conduct the first evolutionary comparison of genome-wide origins maps across vertebrates. Results: We generated a high resolution genome-wide map of chicken replication origins (the first of a bird genome), and performed an extensive comparison with human and mouse maps. The analysis of intra-species polymorphism revealed a strong depletion of genetic diversity on a ∼ 40bp region centered on the replication initiation loci. Surprisingly, this depletion in genetic diversity is not linked to the presence of G4 motifs, nor to the association with promoters or CpG islands. In contrast, we also show that origins have experienced a rapid turnover during vertebrates evolution, since pairwise comparisons of origin maps revealed that only 4 to 24% of them are conserved between any two species. Conclusions: This study unravels the existence of a novel genetic determinant of replication origins, whose precise functional role remains to be determined. Despite the importance of replication initiation activity for the fitness of organisms, the distribution of replication origins along vertebrate chromosomes is highly flexible.
Project description:modENCODE_submission_709 This submission comes from a modENCODE project of David MacAlpine. For full list of modENCODE projects, see http://www.genome.gov/26524648 Project Goal: Early origins of replication were identified by treating cells with hydroxyurea (HU), a potent inhibitor of nucleotide synthesis, in the presence of the nucleotide analogue BrdU. Treatment of synchronized Kc167 cells with HU stalls replication forks and activates the intra S-phase checkpoint, thereby limiting BrdU incorporation to those sequences immediately adjacent to early activating replication origins. BrdU enriched sequences surrounding early origins of replication are then enriched by immunoprecipitation with an anti-BrdU antibody. Early origins are then detected by hybridization to Agilent genomic tiling arrays. Peaks are called using MA2C (http://liulab.dfci.harvard.edu/MA2C/MA2C.htm) Keywords: CHIP-chip For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODEDataReleasePolicyFinal2008.pdf EXPERIMENT TYPE: CHIP-chip. BIOLOGICAL SOURCE: Cell Line: Kc167; Tissue: embryo-derived cell-line; Genotype: se/e; Sex: Female NUMBER OF REPLICATES: 4; EXPERIMENTAL FACTORS: Cell Line Kc167
Project description:The budding yeast genome is marked by 250-350 origins of DNA replication. These origins are bound by the origin recognition complex (ORC) throughout the cell cycle. ORC has known DNA binding sequence preferences which, though necessary for binding, are not sufficient to fully specify a genomic locus as being bound by ORC, indicating that the cell must use additional chromosomal cues to specify ORC binding sites and origins of replication. Using high-throughput sequencing to precisely locate both ORC binding sites and nucleosome locations genome-wide, we find that a nucleosome depleted region (NDR) and precisely positioned nucleosomes are a ubiquitous feature of yeast replication origins. The ARS consensus sequence (ACS) and adjacent sequences are sufficient to maintain the nucleosome-free properties of the NDR. We use a temperature sensitive ORC1 mutant to demonstrate that ORC is required to maintain precisely positioned nucleosomes at origins of replication. These findings demonstrate the importance of local nucleosome positioning at replication origins, and that chromatin organization is an important determinant of origin selection.
Project description:modENCODE_submission_709 This submission comes from a modENCODE project of David MacAlpine. For full list of modENCODE projects, see http://www.genome.gov/26524648 Project Goal: Early origins of replication were identified by treating cells with hydroxyurea (HU), a potent inhibitor of nucleotide synthesis, in the presence of the nucleotide analogue BrdU. Treatment of synchronized Kc167 cells with HU stalls replication forks and activates the intra S-phase checkpoint, thereby limiting BrdU incorporation to those sequences immediately adjacent to early activating replication origins. BrdU enriched sequences surrounding early origins of replication are then enriched by immunoprecipitation with an anti-BrdU antibody. Early origins are then detected by hybridization to Agilent genomic tiling arrays. Peaks are called using MA2C (http://liulab.dfci.harvard.edu/MA2C/MA2C.htm) Keywords: CHIP-chip For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODEDataReleasePolicyFinal2008.pdf
Project description:Genomic integrity requires faithful chromosome duplication. Origins of replication are the genomic sites where DNA replication initiates in every cell cycle. There are multiple origins scattered throughout the eukaryotic genome whose genome-wide identification has been a hard challenge, especially in multicellular organisms. Thus, very little is known on the distinctive features of origins in terms of DNA sequence and chromatin context at a genomic scale. Here we have profiled origins in Arabidopsis thaliana by high-throughput sequencing of purified nascent DNA strands. We have identified 1543 replication origins, which were uniformly distributed across the Arabidopsis genome and enriched in binding signals of two replication initiation proteins, CDC6 and ORC1. We have also analyzed novel epigenome maps of various histone modifications and found links between origins and epigenetic signatures, which differ from or have not been reported for other eukaryotic systems. Arabidopsis origins tend to be embedded in G+C-rich regions within the 5M-bM-^@M-^Y half of genes, enriched in histone H2A.Z, H3K4me2/3 and acetylated H4, and depleted of H3K4me1 and H3K9me2. Our data establish the basis for the understanding of the epigenetic specification of origins of replication in Arabidopsis and have implications for the mechanisms of origin specification in other eukaryotes. This SuperSeries is composed of the following subset Series: GSE21781: Mapping origins of replication in Arabidopsis thaliana: Examination of BrdU labelled DNA and unlabelled DNA in one cell type GSE21827: Mapping origins of replication in Arabidopsis thaliana: H3K4ac ChIP vs. unmodified H3 ChIP Refer to individual Series