Collisions between replication and transcription machineries represent a significant source of genomic instability. RECQ5 DNA helicase binds to RNA-polymerase (RNAP) II during transcription elongation and suppresses transcription-associated genomic instability. Here, we show that RECQ5 also associates with RNAPI and enforces the stability of ribosomal DNA arrays. We demonstrate that RECQ5 associates with transcription complexes in DNA replication foci and counteracts replication fork stalling in RNAPI- and RNAPII-transcribed genes, suggesting that RECQ5 exerts its genome-stabilizing effect by acting at sites of replication-transcription collisions. Moreover, RECQ5-deficient cells accumulate RAD18 foci and BRCA1-dependent RAD51 foci that are both formed at sites of interference between replication and transcription and likely represent unresolved replication intermediates. Finally, we provide evidence for a novel mechanism of resolution of replication-transcription collisions wherein the interaction between RECQ5 and proliferating cell nuclear antigen (PCNA) promotes RAD18-dependent PCNA ubiquitination and the helicase activity of RECQ5 promotes the processing of replication intermediates.

Institute of Molecular Cancer Research University of Zurich 8057 Zurich Switzerland

Institute of Molecular Genetics Academy of Sciences of the Czech Republic 142 20 Prague Czech Republic

Institute of Molecular Genetics Academy of Sciences of the Czech Republic 142 20 Prague Czech Republic Genome Integrity Unit Danish Cancer Society Research Center 2100 Copenhagen Denmark Department of Medical Biochemistry and Biophysics Karolinska Institute 17177 Stockholm Sweden

Institute of Molecular Genetics Academy of Sciences of the Czech Republic 142 20 Prague Czech Republic Institute of Molecular Cancer Research University of Zurich 8057 Zurich Switzerland

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RAD51 Inhibition Induces R-Loop Formation in Early G1 Phase of the Cell Cycle

Single-molecule visualization of human RECQ5 interactions with single-stranded DNA recombination intermediates

RECQ5: A Mysterious Helicase at the Interface of DNA Replication and Transcription