SHC1, a high pH inducible gene required for growth at alkaline pH in Saccharomyces cerevisiae

In this study, we carried out a large-scale transposon tagging screening to identify genes whose expression is regulated by ambient pH. Of 35,000 transformants, two strains carrying the genes whose expression is strictly dependent on pH of growth medium were identified. One of the genes with 20-fold induction by alkali pH was identified as SHC1 gene in the Yeast Genome Directory and its expression was the highest at alkaline pH and moderately induced by osmotic stress. However, the gene was expressed neither at acidic pH nor by other stress conditions. The haploid mutant with truncated shc1 gene showed growth retardation and an abnormal morphology at alkaline pH. On the other hand, the mutant strain carrying the wild-type SHC1 gene reverted to the mutant phenotype. To confirm that Shc1p is an alkali-inducible protein, a monoclonal antibody to Shc1p was produced. While a 55-kDa protein band appeared on the Western blot of cells grown at alkaline pH, Shc1p was barely detectable on the blots of cells grown in YPD. Our results indicate that yeast cells have an efficient system adapting to large variations in ambient pH and SHC1 is one of the genes required for the growth at alkaline pH. (C) 1999 Academic Press.