Rabbit sarcoplasmic reticulum Ca2+-ATPase replaces yeast PMC1 and PMR1 Ca2+-ATPases for cell viability and calcineurin-dependent regulation of calcium tolerance

SERcA1a, the fast-twitch skeletal muscle isoform of sarco(endo)plasmic reti culum Ca2+-ATPase, was expressed in yeast using the promoter of the plasma membrane H+-ATPase. In the yeast Saccharomyces cerevisiae, the Golgi PMR1 C a2+-ATPase and the vacuole PMC1 Ca2+-ATPase function together in Ca2+ seque stration and Ca2+ tolerance. SERCA1a expression restored growth of pmc1 mut ants in media containing high Ca2+ concentrations, consistent with increase d Ca2+ uptake in an internal compartment. SERCA1a expression also prevented synthetic lethality of pmr1 pmc1 double mutants on standard media, Electro n microscopy and subcellular fractionation analysis showed that SERCA1a was localized in intracellular membranes derived from the endoplasmic reticulu m, Finally, we found that SERCA1a ATPase activity expressed in yeast was re gulated by calcineurin, a Ca2+/calmodulin-dependent phosphoprotein phosphat ase, This result indicates that calcineurin contributes to calcium homeosta sis by modulating the ATPase activity of Ca2+ pumps localized in intracellu lar compartments.