ISSN:
1574-6968
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
The PMR1 gene of Saccharomyces cerevisiae is thought to encode a putative Ca2+-ATPase [1]. 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 Ca2+-ATPase of the Golgi and Golgi-like membranes. Surprisingly, the pmr1 null mutation abolished Ca2+-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 Ca2+-ATPase is localized in Golgi and/or Golgi-like membranes. Moreover, a third Ca2+-ATPase is found in the ER and ER-like membranes. The data are consistent with the assumption that these Ca2+-ATPases are encoded by gene(s) different from PMR1. Disruption of PMR1 Ca2+-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 Ca2+-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 Ca2+-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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1574-6968.1998.tb12982.x
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