A NOVEL GENE, STT4, ENCODES A PHOSPHATIDYLINOSITOL 4-KINASE IN THE PKC1 PROTEIN-KINASE PATHWAY OF SACCHAROMYCES-CEREVISIAE

A staurosporine-sensitive mutation (stt1) in yeast has been found in t he PKC1 gene that encodes a protein kinase C homologue (Yoshida, S., I keda, E., Uno, I., and Mitsuzawa, H. (1992) Mol. Gen. Genet. 231, 337- 344). We report here another staurosporine-sensitive mutant, stt4, whi ch shows very similar phenotypes to that of the stt1 mutant. The stt4 temperature-sensitive mutant arrests mostly in G2/M phase at 37-degree s-C, and the stt4 deletion mutant shows an osmoremedial phenotype. Sta urosporine sensitivity of the stt4 mutant was suppressed by overexpres sion of PKC1/STT1, indicating genetic interaction between stt4 and pkc 1/stt1. The nucleotide sequenee of STT4 predicts a hydrophilic protein composed of 1,900 amino acid residues, with 26% sequence identity to the yeast VPS34 gene product and 27% to the catalytic subunit of mamma lian phosphatidylinositol (PI) 3-kinase, respectively. Cell homogenate s of the stt4 deletion mutant show normal PI3-kinase activity but lack most of the PI4-kinase activity that is detected in the wild-type. We conclude that STT4 encodes a yeast PI4-kinase that functions in the P KC1 protein kinase pathway.