Recombination occurs within minutes of replication blockage by RTS1 producing restarted forks that are prone to collapse

  1. Michael O Nguyen
  2. Manisha Jalan
  3. Carl A Morrow
  4. Fekret Osman
  5. Matthew C Whitby  Is a corresponding author
  1. University of Oxford, United Kingdom

Abstract

The completion of genome duplication during the cell cycle is threatened by the presence of replication fork barriers (RFBs). Following collision with a RFB replication proteins can dissociate from the stalled fork (fork collapse) rendering it incapable of further DNA synthesis unless recombination intervenes to restart replication. We use time-lapse microscopy and genetic assays to show that recombination is initiated within ~10 minutes of replication fork blockage at a site-specific barrier in fission yeast, leading to a restarted fork within ~60 minutes, which is only prevented/curtailed by the arrival of the opposing replication fork. The restarted fork is susceptible to further collapse causing hyper-recombination downstream of the barrier. Surprisingly, in our system fork restart is unnecessary for maintaining cell viability. Seemingly the risk of failing to complete replication prior to mitosis is sufficient to warrant the induction of recombination even though it can cause deleterious genetic change.

Article and author information

Author details

  1. Michael O Nguyen

    Department of Biochemistry, University of Oxford, Oxford, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  2. Manisha Jalan

    Department of Biochemistry, University of Oxford, Oxford, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  3. Carl A Morrow

    Department of Biochemistry, University of Oxford, Oxford, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  4. Fekret Osman

    Department of Biochemistry, University of Oxford, Oxford, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  5. Matthew C Whitby

    Department of Biochemistry, University of Oxford, Oxford, United Kingdom
    For correspondence
    matthew.whitby@bioch.ox.ac.uk
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Stephen C Kowalczykowski, University of California, Davis, United States

Publication history

  1. Received: August 28, 2014
  2. Accepted: March 24, 2015
  3. Accepted Manuscript published: March 25, 2015 (version 1)
  4. Version of Record published: April 23, 2015 (version 2)

Copyright

© 2015, Nguyen et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Michael O Nguyen
  2. Manisha Jalan
  3. Carl A Morrow
  4. Fekret Osman
  5. Matthew C Whitby
(2015)
Recombination occurs within minutes of replication blockage by RTS1 producing restarted forks that are prone to collapse
eLife 4:e04539.
https://doi.org/10.7554/eLife.04539
  1. Further reading

Further reading

    1. Chromosomes and Gene Expression
    Manisha Jalan, Judith Oehler ... Matthew C Whitby
    Research Advance Updated

    Homologous recombination helps ensure the timely completion of genome duplication by restarting collapsed replication forks. However, this beneficial function is not without risk as replication restarted by homologous recombination is prone to template switching (TS) that can generate deleterious genome rearrangements associated with diseases such as cancer. Previously we established an assay for studying TS in Schizosaccharomyces pombe (Nguyen et al., 2015). Here, we show that TS is detected up to 75 kb downstream of a collapsed replication fork and can be triggered by head-on collision between the restarted fork and RNA Polymerase III transcription. The Pif1 DNA helicase, Pfh1, promotes efficient restart and also suppresses TS. A further three conserved helicases (Fbh1, Rqh1 and Srs2) strongly suppress TS, but there is no change in TS frequency in cells lacking Fml1 or Mus81. We discuss how these factors likely influence TS.

    1. Chromosomes and Gene Expression
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    Research Article

    Kinetoplastids are a highly divergent lineage of eukaryotes with unusual mechanisms for regulating gene expression. We previously surveyed 65 putative chromatin factors in the kinetoplastid Trypanosoma brucei. Our analyses revealed that the predicted histone methyltransferase SET27 and the Chromodomain protein CRD1 are tightly concentrated at RNAPII transcription start regions (TSRs). Here we report that SET27 and CRD1, together with four previously uncharacterized constituents, form the SET27 promoter-associated regulatory complex (SPARC), which is specifically enriched at TSRs. SET27 loss leads to aberrant RNAPII recruitment to promoter sites, accumulation of polyadenylated transcripts upstream of normal transcription start sites, and conversion of some normally unidirectional promoters to bidirectional promoters. Transcriptome analysis in the absence of SET27 revealed upregulated mRNA expression in the vicinity of SPARC peaks within the main body of chromosomes in addition to derepression of genes encoding variant surface glycoproteins (VSGs) located in subtelomeric regions. These analyses uncover a novel chromatin-associated complex required to establish accurate promoter position and directionality.