Non-homologous end joining as an important mutagenic process in cell cycle-arrested cells.
Resting cells experience mutations without apparent external mutagenic influences. Such DNA replication-independent mutations are suspected to be a consequence of processing of spontaneous DNA lesions. Using experimental systems based on reversions of frameshift alleles in Saccharomyces cerevisiae, we evaluated the impact of defects in DNA double-strand break (DSB) repair on the frequency of replication-independent mutations. The deletion of the genes coding for Ku70 or DNA ligase IV, which are both obligatory constituents of the non-homologous end joining (NHEJ) pathway, each resulted in a 50% reduction of replication-independent mutation frequency in haploid cells. Sequencing indicated that typical NHEJ-dependent reversion events are small deletions within mononucleotide repeats, with a remarkable resemblance to DNA polymerase slippage errors. Experiments with diploid and RAD52- or RAD54-deficient strains confirmed that among DSB repair pathways only NHEJ accounts for a considerable fraction of replication-independent frameshift mutations in haploid and diploid NHEJ non-repressed cells. Thus our results provide evidence that G(0) cells with unrepressed NHEJ capacity pay for a large-scale chromosomal stability with an increased frequency of small-scale mutations, a finding of potential relevance for carcinogenesis.
Division of Molecular Genetics, Institute of Cancer Research, University of Vienna, Borschkegasse 8a, A-1090 Vienna, Austria. erich.heidenreich@univie.ac.at
Erich
E
Heidenreich
Rene
R
Novotny
Bernd
B
Kneidinger
Veronika
V
Holzmann
Ulrike
U
Wintersberger
D002453:Cell Cycle / Q000235:genetics*; D004249:DNA Damage; D004261:DNA Replication; D006238:Haploidy; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics