STT10, A NOVEL CLASS-D VPS YEAST GENE REQUIRED FOR OSMOTIC INTEGRITY RELATED TO THE PKC1/STT1 PROTEIN-KINASE PATHWAY

We report the genetic and biochemical properties of a staurosporine (ST)- and temperature-sensitive mutant, stt10, of Sacchar omyces cel evisiae. The sttl0 mutant shows an osmoremedial phenotype in a medium with 1 M sorbitol. ST sensitivity of the stt10 mutant was suppressed by overexpression of PKC1/STT1, showing the genetic interactions of STT10 with the PKC1/STT1 pathway. The nucleotide sequence of STT10 predicts a hydrophilic protein composed of 577 amino acids that possesses 20-25% sequence similarity with yeast Slp1/Vam5p, Sec1p and Sly1p, and nematode Unc-18. The stt10 deletion mutant is viable and shows a typical class-D vacuolar protein sorting defective (vps) phenotype. Vacuoles from stt10 cells have a normal vacuolar H+-ATPase activity, but are defective in vacuolar acidification. Genetic studies of yeast mutants carrying Delta stt10, Delta bck1, stt1/pkc1 or stt4 have revealed that their functions are phenotypically related to maintenance of cellular osmotic integrity.