The REG1 Gene Product Is Required for Repression of INO1 and Other Inositol-Sensitive Upstream Activating Sequence-Containing Genes of Yeast

Corresponding author: Susan A. Henry, Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA 15213., sh4b{at}andrew.cmu.edu (E-mail)

Communicating editor: F. WINSTON

A search was conducted for suppressors of the inositol auxotrophic phenotype of the ino4-8 mutant of yeast. The ino4-8 mutation is a single base pair change that results in substitution of lysine for glutamic acid at position 79 in the bHLH domain of the yeast regulatory protein, Ino4p. Ino4p dimerizes with a second bHLH protein, Ino2p, to form a complex that binds to the promoter of the INO1 gene, activating transcription. Of 31 recessive suppressors of ino4-8 isolated, 29 proved to be alleles of a single locus, identified as REG1, which encodes a regulatory subunit of a protein phosphatase involved in the glucose response pathway. The suppressor mutation, sia1-1, identified as an allele of REG1, caused constitutive INO1 expression and was capable of suppressing the inositol auxotrophy of a second ino4 missense mutant, ino4-26, as well as ino2-419, a missense mutation of INO2. The suppressors analyzed were unable to suppress ino2 and ino4 null mutations, but the reg1 deletion mutation could suppress ino4-8. A deletion mutation in the OPI1 negative regulator was incapable of suppressing ino4-8. The relative roles of the OPI1 and REG1 gene products in control of INO1 expression are discussed.

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