A Novel Protein, CSG2p, Is Required for Ca²⁺ Regulation in Saccharomyces cerevisiae

Authors

Troy Beeler, Uniformed Services University of the Health Sciences
Kenneth Gable, Uniformed Services University of the Health Sciences
Chun Zhao, Uniformed Services University of the Health Sciences
Teresa Dunn, Uniformed Services University of the Health Sciences

Date of this Version

1994

Comments

Published in the Journal of Biological Chemistry (1994) 269(10): pp. 7279-7284

Abstract

Nineteen mutants that lost the ability to grow in 100 mM Ca²⁺ (but remained insensitive to 50 mM Sr²⁺) were identified in a screen of approximately 60,000 mutagenized yeast colonies. Cells carrying mutations in the CSG2 gene grow normally in low Ca²⁺ medium but have decreased growth rates when the Ca²⁺ concentration is above 10 mM. The csg2 mutant cells accumulate much higher levels of Ca²⁺ in a compartment that is exchangeable with extracellular Ca²⁺ but the nonexchangeable Ca²⁺ pool which predominates in wild-type cells is not influenced. Sr²⁺ influx is not increased in the csg2 mutant cells. Mg²⁺ decreases the amount of Ca²⁺ in the nonexchangeable pool without influencing the csg2-induced exchangeable Ca²⁺ pool. The data indicate that the csg2 mutation causes a selective increase in Ca²⁺ accumulation into a pool which is distinct from the vacuolar pool. The CSG2 protein consists of 410 amino acids, contains nine putative transmembrane segments, four potential sites for N-linked glycosylation, and a sequence with homology to the EF-hand Ca²⁺-binding site.