Characterization of an allele-nonspecific intragenic suppressor in the yeast plasma membrane H+-ATPase gene (Pma1).

We have analyzed the ability of A165V, V169I/D170N, and P536L mutations to suppress pma1 dominant lethal alleles and found that the P536L mutation is able to suppress the dominant lethality of the pma1-R271T, -D378N, -D378E, and -K474R mutant alleles. Genetic and biochemical analyses of site-directed mutants at Pro-536 suggest that this amino acid may not be essential for function but is important for biogenesis of the ATPase. Proteins encoded by dominant lethal pma1 alleles are retained in the endoplasmic reticulum, thus interfering with transport of wild-type Pma1. Immunofluorescence studies of yeast conditionally expressing revertant alleles show that the mutant enzymes are correctly located at the plasma membrane and do not disturb targeting of the wild-type enzyme. We propose that changes in Pro-536 may influence the folding of the protein encoded by a dominant negative allele so that it is no longer recognized and retained as a misfolded protein by the endoplasmic reticulum.