YEAST SKO1 GENE ENCODES A BZIP PROTEIN THAT BINDS TO THE CRE MOTIF AND ACTS AS A REPRESSOR OF TRANSCRIPTION

We have cloned a yeast gene, SKO1, which in high copy number suppresses lethal overexpression of cAMP-dependent protein kinase. SKO1 encodes a bZIP protein that binds to the CRE motif, TGACGTCA. We found that SKO1 also binds to a CRE-like site in SUC2, a yeast gene encoding invertase which is under positive control by cAMP. A disruption of the SKO1 gene causes a partial derepression of SUC2, indicating that SKO1 is a negative regulator of the SUC2 gene. SKO1 interacts positively with MIG1, a zinc finger protein that mediates glucose repression of SUC2. A kinetic analysis revealed a complex regulation of the SUC2 mRNA in response to glucose. First, MIG1 mediates a rapid and strong repression of SUC2, which is complete within 10 minutes. Second, a MIG1-independent process causes a further slow reduction in the mRNA. Third, in the absence of MIG1, there is also a rapid but transient glucose induction of the SUC2 mRNA. This induction is correlated with a transient loss of SKO1-dependent repression.