CHARACTERIZATION OF DOMINANT LETHAL MUTATIONS IN THE YEAST PLASMA-MEMBRANE H-ATPASE GENE()

Site-directed mutants of yeast ATPase were studied after introduction of mutant alleles into a yeast strain where these alleles mere constit utively expressed and the expression of the wild-type chromosomal ATPa se gene was turned off. One objection to this constitutive expression system was made apparent recently, as dominant lethal mutations are lo st by gene conversion with the wild-type allele during the process. He re, the phenotypes of the mutant alleles, which were studied in a cons titutive expression system, are re-evaluated under conditions in which these site-directed mutants are conditionally expressed. We show that 12 of 25 site-directed mutations previously described are actually do minant lethal alleles. In addition, we show that dominant mutant prote ins interfere with transport of wild-type ATPase to the plasma membran e.