A similar defect in UV-induced mutagenesis conferred by the rad6 and rad18 mutations of Saccharomyces cerevisiae.

The single rad6 and rad18 yeast mutants share a number of physiological and biochemical properties related to DNA repair, suggesting that they affect closely related steps. However, it has been reported that UV-induced mutagenesis is considerably more depressed in rad6 than it is in rad18 cells. In an attempt to better understand the role of these genes, a genetic system believed to differentiate between targeted and untargeted events was used. The data are interpreted to mean that both mutations prevent the occurrence of targeted events, as if they prevent error-prone replication in front of pyrimidine dimers. The number of non-targeted mutants per survivor in each mutant was increased by UV irradiation. This may correspond to a stimulation of the error-prone replication.