ANALYSIS OF THE SPECTRUM OF MUTATIONS INDUCED BY THE RAD3-102 MUTATOR ALLELE OF YEAST

The product of the RAD3 gene of Saccharomyces cerevisiae is required for mitotic cell viability and excision repair of UV-induced pyrimidine dimers. Certain rad3 mutant alleles (originally called rem1) increase the rates of both spontaneous mitotic recombination and mutation. The increase in mutation rates is not dependent upon the presence of the RAD6 error-prone pathway. The mutator phenotype suggests that the wild-type RAD3 gene product may be involved in the maintenance of fidelity of DNA replication in addition to its known role in excision repair. To investigate the role that RAD3 might play in mutation avoidance, we have utilized a well-characterized shuttle vector system to study the mutational spectrum occurring in rad3-102 strains and compare it to that seen in RAD3 strains. The results put constraints on the role that the rad-102 mutant gene product must play if the RAD3 protein is a component of the replication complex. Alternatively. the mutational spectrum is consistent with the hypothesis that the rad3-102 mutant protein interferes with postreplication mismatch repair.