GENETIC ANALYSIS OF MULTIPLE DRUG CROSS RESISTANCE IN SACCHAROMYCES CEREVISIAE: A NUCLEAR-MITOCHONDRIAL GENE INTERACTION

A mutant of the yeast Saccharomyces cereuisiae, cross resistant to several antibiotics, was isolated in our laboratory and subjected to genetic analysis. Tetrad analysis of diploids obtained from crosses between the resistant mutant and a sensitive wild-type strain suggest that the multiple resistance to the five agents, oligomycin (OLI), rhodamine 6G (RHG), tetracycline (TCN), chloramphenicol (CAP) and cycloheximide (CHX) is determined by a single nuclear gene, anti, and requires several cytoplasmic genes for expression of resistance to oligomycin, rhodamine 6G and tetracycline.——Vegetatively growing diploid clones derived from the cross ant1 [RHO+] × + [RHO+] show mitotic segregation of two phenotypic classes for the drugs OLI, RHG TCN. Diploids derived from the two reciprocal crosses, ant1 [RHO+] × + [RHO-] and ant1 [RHO-] × + [RHO+], fail to exhibit mitotic segregation. These results are consistent with our hypothesis concerning the involvement of cytoplasmic loci. They suggest, in addition, that these loci are associated with mitochondrial DNA (mtDNA) .——Evidence for this association is provided by the demonstration of genetic linkage between the cytoplasmic loci involved in the interaction, RHG-1, TCN-1 and OLI-5, and two well-characterized mitochondrial loci, ERY and CAP.——We have mapped the nuclear ant1 locus 3.3 cM from the centromere-linked gene, leu1, on the same side of the centromere of chromosome VII as leu1.——In the light of these findings, we discuss the claims made by several authors of the episomal nature of mutations similar ta the one described here, as well as of the possible involvement of yeast 2μ DNA in such mutations.