Yeast Mutants Affecting Possible Quality Control of Plasma Membrane Proteins

Abstract

Mutations gef1, stp22, STP26, and STP27 in Saccharomyces cerevisiae were identified as suppressors of the temperature-sensitive α-factor receptor (mutation ste2-3) and arginine permease (mutation can1^ts). These suppressors inhibited the elimination of misfolded receptors (synthesized at 34°C) as well as damaged surface receptors (shifted from 22 to 34°C). The stp22 mutation (allelic to vps23 [M. Babst and S. Emr, personal communication] and the STP26mutation also caused missorting of carboxypeptidase Y, and ste2-3 was suppressed by mutations vps1,vps8, vps10, and vps28 but not by mutation vps3. In the stp22 mutant, both the mutant and the wild-type receptors (tagged with green fluorescent protein [GFP]) accumulated within an endosome-like compartment and were excluded from the vacuole. GFP-tagged Stp22p also accumulated in this compartment. Upon reaching the vacuole, cytoplasmic domains of both mutant and wild-type receptors appeared within the vacuolar lumen. Stp22p and Gef1p are similar to tumor susceptibility protein TSG101 and voltage-gated chloride channel, respectively. These results identify potential elements of plasma membrane quality control and indicate that cytoplasmic domains of membrane proteins are translocated into the vacuolar lumen.

ACKNOWLEDGMENTS

We thank S. Emr, R. Gilmore, J. Haber, J. Konopka, C. Raymond, S. Rieder, and T. Stevens for providing antisera and plasmids. We also thank M. Babst and S. Emr for communicating unpublished results and Ayce Yesilaltay, Aidan Hennigan, and Jodi Hirschman for comments on the manuscript.

This investigation was supported by grant VM-31 from the American Cancer Society and by Public Health Service research grant GM34719 from the National Institute of General Medical Sciences.