Author(s): Okorokov LA, Lehle L
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Abstract The PMR1 gene of Saccharomyces cerevisiae is thought to encode a putative Ca(2+)-ATPase . Membranes isolated from wild-type cells and from pmr1 null mutant of S. cerevisiae were fractionated on sucrose density gradients. In the pmr1 mutant we found a decrease in activity of the P-type ATPase and of ATP-dependent, protonophore-insensitive Ca2+ transport in light membranes, that comigrate with the Golgi marker GDPase. We conclude that the product of the PMR1 gene (Pmr1p) is indeed a Ca(2+)-ATPase of the Golgi and Golgi-like membranes. Surprisingly, the pmr1 null mutation abolished Ca(2+)-ATPase activity in Golgi and/or Golgi-like membranes only to 50\% under conditions where they are separated from vacuolar membranes. This indicates that an additional Ca(2+)-ATPase is localized in Golgi and/or Golgi-like membranes. Moreover, a third Ca(2+)-ATPase is found in the ER and ER-like membranes. The data are consistent with the assumption that these Ca(2+)-ATPases are encoded by gene(s) different from PMR1. Disruption of PMR1 Ca(2+)-ATPase causes significant redistribution of enzyme activities and of total protein in compartments of the secretory pathway. A decrease in activity is observed for three integral membrane proteins: NADPH cytochrome c reductase, dolichyl phosphate mannose synthase, and Ca(2+)-ATPase, and also for total protein in Golgi, Golgi-like compartments and in vacuoles, whereas a corresponding increase of these activities is observed in endoplasmic reticulum and endoplasmic reticulum-like membranes. We assume that Ca(2+)-ATPases and sufficient Ca2+ gradients across the organellar membranes are important for the correct sorting of proteins to the various compartments of the secretory apparatus.
This article was published in FEMS Microbiol Lett
and referenced in Journal of Pulmonary & Respiratory Medicine