The unusual inheritance of multidrug-resistance factors in Saccharomyces.

The yeast PDR5 locus encodes a 160-kDa member of the ABC family of transport proteins. Strains bearing a deletion of this locus are drug hypersensitive. Resistant revertants arise when cells are plated on cycloheximide medium. About one-third of these are cross resistant to other agents, including oligomycin, fluconazole and sulfometuron methyl. Most of the revertants exhibit linkage to the PDR5 locus and map in three locations. Curiously, the multi-drug resistance is not due to a single mutation. Most of the revertants behave as though they contained several tightly linked resistance factors.