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DDX17 helicase promotes resolution of R-loop-mediated transcription-replication conflicts in human cells

ABSTRACT: R-loops are three-stranded nucleic acid structures composed of an RNA:DNA hybrid and displaced DNA strand. These structures can halt DNA replication when formed co- transcriptionally in the opposite orientation to replication fork progression. Recent studies have shown that replication forks stalled by co-transcription R-loops can be restarted by a mechanism involving fork cleavage by MUS81 endonuclease, followed by reactivation of transcription, and fork religation by the DNA ligase IV (LIG4)/XRCC4 complex. However, how R-loops are eliminated to allow the sequential restart of transcription and replication in this pathway remains elusive. Here, we identified the human DDX17 helicase as a factor that associates with R-loops and counteracts R-loop-mediated replication stress to preserve genome stability. We show that DDX17 unwinds RNA:DNA hybrids in vitro and promotes MUS81-dependent restart of R-loop-stalled forks in human cells in a manner dependent on its helicase activity. Loss of DDX17 helicase induces accumulation of R-loops and the formation of R-loop-dependent anaphase bridges and micronuclei. These findings establish DDX17 as a component of the MUS81-LIG4 pathway for resolution of R-loop-mediated transcription- replication conflicts, which may be involved in R-loop unwinding.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Pavel Talacko

LAB HEAD: Pavel Janscak

PROVIDER: PXD034331 | Pride | 2022-11-02

REPOSITORIES: Pride

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Project description:Background: Chromatin remodeling complexes facilitate the access of enzymes that mediate transcription, replication or repair of DNA by modulating nucleosome position and/or composition. Ino80 is the DNA-dependent Snf2-like ATPase subunit of a complex whose nucleosome remodeling activity requires actin-related proteins, Arp4, Arp5 and Arp8, as well as two RuvB-like DNA helicase subunits. Budding yeast mutants deficient for Ino80 function are not only hypersensitive to reagents that induce DNA double strand breaks, but also to those that impair replication fork progression. Results: To understand why ino80 mutants are sensitive to agents that perturb DNA replication, we used chromatin immunoprecipitation to map the binding sites of the Ino80 chromatin remodeling complex on four budding yeast chromosomes. We found that Ino80 and Arp5 binding sites coincide with origins of DNA replication and tRNA genes. In addition, Ino80 was bound at 67% of the promoters of genes that are sensitive to ino80 mutation. When replication forks were arrested near origins in the presence of hydroxyurea (HU), the presence of the Ino80 complex at stalled forks and at unfired origins increased dramatically. Importantly, the resumption of DNA replication after release from a HU block was impaired in the absence of Ino80 activity. Mutant cells accumulated double-strand breaks as they attempted to restart replication. Consistently, ino80-deficient cells, although proficient for checkpoint activation, delay recovery from the checkpoint response. Conclusions: The Ino80 chromatin remodeling complex is enriched at stalled replication forks where it promotes the resumption of replication upon recovery from fork arrest. Keywords: ChIP-chip • The goal of the experiment Genome-wide localization of Ino80 on chromosome in Saccharomyces cerevisiae • Keywords DNA replication, Saccharomyces cerevisiae, Genome tilling array (chromosome III, IV, V, VI) • Experimental factor Distribution of Ino80 in random culture Distribution of Ino80 in G1 phase Distribution of Ino80 in early S phase • Experimental design ChIP analyses: W303 background cells expressing Myc-tagged Ino80 were used for the ChIP using anti-Myc monoclonal antibody (9E11). ChIP-chip analyses: In all cases, hybridization data for ChIP fraction was compared with WCE (whole cell extract) fraction. Saccharomyces cerevisiae affymetrix genome tiling array (SC3456a520015F for chromosome III, IV, V, VI) was used. • Quality control steps taken Confirmation of several loci by quantitative real time PCR.

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DDX17 helicase promotes resolution of R-loop-mediated transcription-replication conflicts in human cells

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