The pol3-t Hyperrecombination Phenotype and DNA Damage-Induced Recombination in Saccharomyces cerevisiae Is RAD50 Dependent

Abstract EN

The DNA polymerase δ (POL3/CDC2) allele pol3-t of Saccharomyces cerevisiae has previously been shown to be sensitive to methylmethanesulfonate (MMS) and has been proposed to be involved in base excision repair.

Our results, however, show that the pol3-t mutation is synergistic for MMS sensitivity with MAG1, a known base excision repair gene, but it is epistatic with rad50Δ, suggesting that POL3 may be involved not only in base excision repair but also in a RAD50 dependent function.

We further studied the interaction of pol3-t with rad50Δ by examining their effect on spontaneous, MMS-, UV-, and ionizing radiation-induced intrachromosomal recombination.

We found that rad50Δ completely abolishes the elevated spontaneous frequency of intrachromosomal recombination in the pol3-t mutant and significantly decreases UV- and MMS-induced recombination in both POL3 and pol3-t strains.

Interestingly, rad50Δ had no effect on γ-ray-induced recombination in both backgrounds between 0 and 50 Gy.

Finally, the deletion of RAD50 had no effect on the elevated frequency of homologous integration conferred by the pol3-t mutation.

RAD50 is possibly involved in resolution of replication forks that are stalled by mutagen-induced external DNA damage, or internal DNA damage produced by growing the pol3-t mutant at the restrictive temperature.