Cloning by gene amplification of two loci conferring multiple drug resistance in Saccharomyces

Yeast DNA fragments that confer multiple drug resistance when amplified were isolated. Cells containing a yeast genomic library cloned in the high copy autonomously replicating vector, YEp24, were plated on medium containing cycloheximide. Five out of 100 cycloheximide-resistant colonies were cross-resistant to the unrelated inhibitor, sulfometuron methyl, due to a plasmid-borne resistance determinant. The plasmids isolated from these resistant clones contained two nonoverlapping regions in the yeast genome now designated PDR4 and PDR5 (for pleiotropic drug resistant). PDR4 was mapped to chromosome XIII, 31.5 cM from LYS7 and 9 cM from the centromere. PDR4 was mapped to chromosome XV between ADE2 and H1S3. Genetic analysis demonstrated that at least three tightly linked genes (PDR5, PDR2 and SMR3) that mediate resistance to inhibitors are located in this region. Insertion mutations in the either PDR4 or PDR5 genes are not lethal, but the insertion in PDR5 results in a drug-hypersensitive phenotype.