CLONING AND SEQUENCE OF THE SCS2 GENE, WHICH CAN SUPPRESS THE DEFECT OF INO1 EXPRESSION IN AN INOSITOL AUXOTROPHIC MUTANT OF SACCHAROMYCES-CEREVISIAE

Saccharomyces cerevisiae ire15 mutant has a defect in the expression o f INO1, showing the inositol auxotrophic phenotype [Nikawa, J. (1994) Gene 149, 367-372]. We have isolated five yeast genes which suppress t he ire15 mutation in multiple copies by genetic complementation. Among them, one gene, designated as SCS2, also suppressed the choline-sensi tive dominant mutation, CSE1 [Hosaka, K. et al. (1992) J. Biochem. 111 , 352-358]. The CSE1 mutation is not allelic to ire15. Sequencing anal ysis revealed that the SCS2 gene encodes 244 amino acid residues with a calculated molecular mass of 26,866, INO2/SCS1, which is another sup pressor gene for CSE1 and is known to be a positive factor for INO1 ex pression, also suppressed the growth defect of the ire15 mutant, These results clearly indicate that the ire15 and CSE1 mutations geneticall y interact and the SCS2 and INO2/SCS1 genes are involved in the regula tion of INO1 expression.