STT3, a novel essential gene related to the PKC1/STT1 protein kinase pathway, is involved in protein glycosylation in yeast.

Mutations of genes involved in the STT1/PKC1 pathway in yeast show staurosporine and temperature sensitivities (stt) which are suppressed by the addition of 1 M sorbitol [Yoshida et al., Mol. Gen. Genet. 242 (1994) 631-640]. Among the stt mutants, stt3-2 shares this phenotype. The STT3 gene encodes a novel 718-amino-acid protein with significant homology to potential transmembrane proteins of Caenorhabditis elegans and mouse mandibular condyle (about 80% homologous and 60% identical). Unlike the STT1/PKC1 gene, STT3 is essential for cell growth irrespective of osmotic support. Pulse-chase experiments show that the sst3 mutants are defective in protein glycosylation. The stt3 mutants are sensitive to hygromycin B and resistant to sodium orthovanadate, whose phenotypes are common to those defective in protein glycosylation.