• Reference Type: Journal Article
  Kaniecki K, et al. (2017) Dissociation of Rad51 Presynaptic Complexes and Heteroduplex DNA Joints by Tandem Assemblies of Srs2. Cell Rep 21(11):3166-3177 PMID: 29241544
  • SGD Paper
  • DOI full text
  • PMC full text
  • PubMed

  Srs2 is a superfamily 1 (SF1) helicase and antirecombinase that is required for genome integrity. However, the mechanisms that regulate Srs2 remain poorly understood. Here, we visualize Srs2 as it acts upon single-stranded DNA (ssDNA) bound by the Rad51 recombinase. We demonstrate that Srs2 is a processive translocase capable of stripping thousands of Rad51 molecules from ssDNA at a rate of ∼50 monomers/s. We show that Srs2 is recruited to RPA clusters embedded between Rad51 filaments and that multimeric arrays of Srs2 assemble during translocation on ssDNA through a mechanism involving iterative Srs2 loading events at sites cleared of Rad51. We also demonstrate that Srs2 acts on heteroduplex DNA joints through two alternative pathways, both of which result in rapid disruption of the heteroduplex intermediate. On the basis of these findings, we present a model describing the recruitment and regulation of Srs2 as it acts upon homologous recombination intermediates.

• Reference Type: Journal Article
  De Tullio L, et al. (2017) Yeast Srs2 Helicase Promotes Redistribution of Single-Stranded DNA-Bound RPA and Rad52 in Homologous Recombination Regulation. Cell Rep 21(3):570-577 PMID: 29045827
  • SGD Paper
  • DOI full text
  • PMC full text
  • PubMed

  Srs2 is a super-family 1 helicase that promotes genome stability by dismantling toxic DNA recombination intermediates. However, the mechanisms by which Srs2 remodels or resolves recombination intermediates remain poorly understood. Here, single-molecule imaging is used to visualize Srs2 in real time as it acts on single-stranded DNA (ssDNA) bound by protein factors that function in recombination. We demonstrate that Srs2 is highly processive and translocates rapidly (∼170 nt per second) in the 3'→5' direction along ssDNA saturated with replication protein A (RPA). We show that RPA is evicted from DNA during the passage of Srs2. Remarkably, Srs2 also readily removes the recombination mediator Rad52 from RPA-ssDNA and, in doing so, promotes rapid redistribution of both Rad52 and RPA. These findings have important mechanistic implications for understanding how Srs2 and related nucleic acid motor proteins resolve potentially pathogenic nucleoprotein intermediates.

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