The pso mutants of Saccharomyces cerevisiae comprise two groups: one deficient in DNA repair and another with altered mutagen metabolism

Yeast mutants that are sensitive to photoactivated psoralens, named pso mut ants, were isolated and described more than 20 years ago. Nine genes respon sible for the pso phenotypes were identified and seven of them cloned and m olecularly characterized. Of the nine PSO genes of yeast seven apparently e ncode proteins involved in the repair of DNA lesions generated by photoindu ced psoralens and by other mutagens, while two, PSO6 and PSO7, are responsi ble for structural elements of the membrane and for a functional respirator y chain, respectively. Of the seven proven or putative DNA repair genes six directly or indirectly control induced mutagenesis. Four of these PSO loci were found allelic to already known repair genes, whereas two, PSO2 and PS O4, represent new genes involved in DNA repair and in repair/pre-mRNA proce ssing in S. cerevisiae. Gene PSO2 encodes a protein indispensable for repai r of DNA interstrand cross-links that are produced by a variety of bi- and poly-functional mutagens and that appears to be important for a likewise re pair function in humans as well. (C) 2001 Published by Elsevier Science B.V .