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 were constitutively expressed and the expression of the wild-type chromosomal ATPase gene was turned off. One objection to this constitutive expression system was made apparent recently, as dominant lethal mutations are lost by gene conversion with the wild-type allele during the process. Here, the phenotypes of the mutant alleles, which were studied in a constitutive 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 dominant lethal alleles. In addition, we show that dominant mutant proteins interfere with transport of wild-type ATPase to the plasma membrane.