Two nuclear proteins, Cin5 and Ydr259c, confer resistance to cisplatin in Saccharomyces cerevisiae

In an attempt to identify genes that can confer resistance to cisplatin, we introduced a yeast genomic library into Saccharomyces cerevisiae and selec ted for transformants that grew in the presence of a normally toxic concent ration of cisplatin. Plasmids were rescued from the transformants and were analyzed for the presence of individual open reading frames that conferred resistance to cisplatin. We isolated two genes, CIN5 and YDR259c, that incr eased resistance to cisplatin when overexpressed in Saccharomyces cerevisia e. These genes encoded two proteins, Cin5 and Ydr259c, that were homologous to yAP-1, a basic leucine zipper transcriptional factor that is known to m ediate cellular resistance to various toxic agents. The two proteins exhibi ted stronger homology to each other (33.2% identity, 49.2% similarity) than to all other gene products in S. cerevisiae. Overexpression of each of the se proteins also conferred resistance to two DNA-alkylating agents, methylm ethanesulfonate and mitomycin C. An experiment with fusion proteins with gr een fluorescent protein revealed that Cin5 and Ydr259c were localized const itutively in the nuclei of yeast cells. Our results suggest that Cin5 and Y dr259c might be involved in pleiotropic drug-resistance and might protect y east against the toxicity of cisplatin and other alkylating agents via a si ngle mechanism. These two nuclear proteins might act as transcriptional fac tors, regulating the expression of certain genes that confer resistance to DNA-alkylating agents.