The yeast secretory pathway is perturbed by mutations in PMR1, a member of a Ca2+ ATPase family

The genes for two new P-type ATPases, PMR1 and PMR2, have been identified in yeast. A comparison of the deduced sequences of the PMR proteins with other known ion pumps showed that both proteins are very similar to Ca2+ ATPases. PMR1 is identical to SSC1, a gene previously identified by its effect on secretion of some foreign proteins from yeast. Proteins secreted from pmr1 mutants lack the outer chain glycosylation that normally results from passage through the Golgi. Loss of PMR1 function suppresses the lethality of ypt1-1, a mutation that blocks the secretion pathway. These data suggest that PMR1 functions as a Ca2+ pump affecting transit through the secretory pathway.