Project description:Background G-quadruplexes (G4s) are stable non-canonical DNA secondary structures consisting of stacked arrays of four guanines, each held together by Hoogsteen hydrogen bonds. Sequences with the ability to form these structures in vitro, G4 motifs, are found throughout bacterial and eukaryotic genomes. The budding yeast Pif1 DNA helicase, as well as several bacterial Pif1 family helicases, unwind G4 structures robustly in vitro and suppress G4-induced DNA damage in S. cerevisiae in vivo. Results We determined the genomic distribution and evolutionary conservation of G4 motifs in four fission yeast species and investigated the relationship between G4 motifs and Pfh1, the sole S. pombe Pif1 family helicase. Using chromatin immunoprecipitation combined with deep sequencing, we found that many G4 motifs in the S. pombe genome were associated with Pfh1. Cells depleted of Pfh1 had increased fork pausing and DNA damage near G4 motifs, as indicated by high DNA polymerase occupancy and phosphorylated histone H2A, respectively. In general, G4 motifs were underrepresented in genes. However, Pfh1-associated G4 motifs were located on the transcribed strand of highly transcribed genes significantly more often than expected, suggesting that Pfh1 has a function in replication or transcription at these sites. Conclusions In the absence of functional Pfh1, unresolved G4 structures cause fork pausing and DNA damage of the sort associated with human tumors.
Project description:G-quadruplex (or G4) structures are non-canonical DNA structures that form in guanine-rich sequences and threaten genome stability when not properly resolved. G4 unwinding occurs during S phase via an unknown mechanism. Using Xenopus egg extracts, we define a three-step G4 unwinding mechanism that acts during DNA replication. First, the replicative helicase (CMG) stalls at a leading strand G4 structure. Second, the DHX36 helicase mediates the bypass of the CMG past the intact G4 structure, which allows approach of the leading strand to the G4. Third, G4 structure unwinding by the FANCJ helicase enables the DNA polymerase to synthesize past the G4 motif. A G4 on the lagging strand template does not stall CMG, but still requires active DNA replication for unwinding. DHX36 and FANCJ have partially redundant roles, conferring robustness to this pathway. Our data reveal a novel genome maintenance pathway that promotes faithful G4 replication thereby avoiding genome instability.
Project description:Analysis of topoisomerase function in bacterial replication fork movement: use of DNA microarrays. We used DNA microarrays of the Escherichia coli genome to trace the progression of chromosomal replication forks in synchronized cells. We found that both DNA gyrase and topoisomerase IV (topo IV) promote replication fork progression. When both enzymes were inhibited, the replication fork stopped rapidly. The elongation rate with topo IV alone was 1/3 of normal. Genetic data confirmed and extended these results. Inactivation of gyrase alone caused a slow stop of replication. Topo IV activity was sufficient to prevent accumulation of (+) supercoils in plasmid DNA in vivo, suggesting that topo IV can promote replication by removing (+) supercoils in front of the chromosomal fork. This study is detailed in Khodursky AB et al.(2000) Proc Natl Acad Sci U S A 97:9419-24 Keywords: other
Project description:Sequencing of mononucleosomal DNA during asynchronous mitosis in Schizosaccharomyces pombe, Schizosaccharomyces octosporus, Schizosaccharomyces japonicus and Saccharomyces cerevisiae
Project description:Analysis of topoisomerase function in bacterial replication fork movement: use of DNA microarrays. We used DNA microarrays of the Escherichia coli genome to trace the progression of chromosomal replication forks in synchronized cells. We found that both DNA gyrase and topoisomerase IV (topo IV) promote replication fork progression. When both enzymes were inhibited, the replication fork stopped rapidly. The elongation rate with topo IV alone was 1/3 of normal. Genetic data confirmed and extended these results. Inactivation of gyrase alone caused a slow stop of replication. Topo IV activity was sufficient to prevent accumulation of (+) supercoils in plasmid DNA in vivo, suggesting that topo IV can promote replication by removing (+) supercoils in front of the chromosomal fork. This study is detailed in Khodursky AB et al.(2000) Proc Natl Acad Sci U S A 97:9419-24 Keywords: other
Project description:Schizosaccharomyces pombe Rad3 checkpoint kinase and its human ortholog ATR are essential for maintaining genome integrity in cells treated with genotoxins that damage DNA or arrest replication forks. Rad3 and ATR also function during unperturbed growth, although the events triggering their activation and their critical functions are largely unknown. Here, we use ChIP-on-chip analysis to map genomic loci decorated by phosphorylated histone H2A (gH2A), a Rad3 substrate that establishes a chromatin-based recruitment platform for DNA repair/checkpoint proteins. Our data showed that gH2A marks a diverse array of genomic features during S-phase, including natural replication fork barriers and a fork breakage site, retrotransposons, heterochromatin in the centromeres and telomeres, and ribosomal RNA (rDNA) repeats. The enrichment of gH2A at these sites was confirmed by multiple ChiP-qPCR experiments.
Project description:Sequencing of mononucleosomal DNA during asynchronous mitosis in Schizosaccharomyces pombe, Schizosaccharomyces octosporus, Schizosaccharomyces japonicus and Saccharomyces cerevisiae Samples from mononucleosomal DNA from asynchronous mitosis of four species of budding (Saccharomyces cerevisiae W303-1a) and fission yeasts (S. pombe wild type 972h-, S. octosporus CBS1804, S. japonicus var. japonicus ade12- FY53) were sequenced (Illumina Genome Analyzer IIx and HiSeq 2500) using the single read and paired end protocol.
Project description:Expression profile of mutant cells compared to wild-type cells: Expression profile of Schizosaccharomyces pombe genome in ∆pht1, ∆ago1, ∆clr4, rik1, ∆pht1rik1, ∆pht1∆ago1 and ∆pht1∆clr4 cells. Expression profile of Schizosaccharomyces pombe genome in ∆rrp6, ∆cid14, ∆swi6, ∆swr1, ∆set1, ∆pht1∆swi6 and ∆pht1∆set1 cells. Expression profile of Schizosaccharomyces pombe genome in ∆alp13, ∆cph1, ∆set2, clr6-1 and ∆cph1∆pht1 cells. Occupancy profiling: Occupancy profiling of RNA polymerase II, histone variant H2A.Z and ClrC subunit Rik1 in fission yeast Schizosaccharomyces pombe Occupancy profiling of histone variant H2A.Z in ∆msc1 cells.