CHARACTERIZATION OF AN ALLELE-NONSPECIFIC INTRAGENIC SUPPRESSOR IN THE YEAST PLASMA-MEMBRANE H-ATPASE GENE (PMA1)()

We have analyzed the ability of A165V, V163I/D170N, and P536L mutation s to suppress pma1 dominant lethal alleles and found that the P536L mu tation is able to suppress the dominant lethality of the pma1-R271T, - D378N, -D378E, and -K474R mutant alleles. Genetic and biochemical anal yses of site-directed mutants at Pro-536 suggest that this amino acid may not be essential for function but is important for biogenesis of t he ATPase. Proteins encoded by dominant lethal pma1 alleles are retain ed in the endoplasmic reticulum, thus interfering with transport of wi ld-type Pma1. Immunofluorescence studies of yeast conditionally expres sing revertant alleles show that the mutant enzymes are correctly loca ted at the plasma membrane and do not disturb targeting of the wild-ty pe enzyme. We propose that changes in Pro-536 may influence the foldin g of the protein encoded by a dominant negative allele so that it is n o longer recognized and retained as a misfolded protein by the endopla smic reticulum.