Homologous recombination rescues ssDNA gaps generated by nucleotide excision repair and reduced translesion DNA synthesis in yeast G2 cells

Proc Natl Acad Sci U S A. 2013 Jul 30;110(31):E2895-904. doi: 10.1073/pnas.1301676110. Epub 2013 Jul 15.

Abstract

Repair of DNA bulky lesions often involves multiple repair pathways such as nucleotide-excision repair, translesion DNA synthesis (TLS), and homologous recombination (HR). Although there is considerable information about individual pathways, little is known about the complex interactions or extent to which damage in single strands, such as the damage generated by UV, can result in double-strand breaks (DSBs) and/or generate HR. We investigated the consequences of UV-induced lesions in nonreplicating G2 cells of budding yeast. In contrast to WT cells, there was a dramatic increase in ssDNA gaps for cells deficient in the TLS polymerases η (Rad30) and ζ (Rev3). Surprisingly, repair in TLS-deficient G2 cells required HR repair genes RAD51 and RAD52, directly revealing a redundancy of TLS and HR functions in repair of ssDNAs. Using a physical assay that detects recombination between circular sister chromatids within a few hours after UV, we show an approximate three-fold increase in recombinants in the TLS mutants over that in WT cells. The recombination, which required RAD51 and RAD52, does not appear to be caused by DSBs, because a dose of ionizing radiation producing 20 times more DSBs was much less efficient than UV in producing recombinants. Thus, in addition to revealing TLS and HR functional redundancy, we establish that UV-induced recombination in TLS mutants is not attributable to DSBs. These findings suggest that ssDNA that might originate during the repair of closely opposed lesions or of ssDNA-containing lesions or from uncoupled replication may drive recombination directly in various species, including humans.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • DNA Breaks, Single-Stranded / radiation effects*
  • DNA Repair / genetics
  • DNA Repair / radiation effects*
  • DNA, Fungal / genetics
  • DNA, Fungal / metabolism*
  • DNA, Single-Stranded / genetics
  • DNA, Single-Stranded / metabolism*
  • G2 Phase / genetics
  • G2 Phase / radiation effects*
  • Humans
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Ultraviolet Rays*

Substances

  • DNA, Fungal
  • DNA, Single-Stranded
  • Saccharomyces cerevisiae Proteins