DUAL INFLUENCE OF THE YEAST CAT1P (SNF1P) PROTEIN-KINASE ON CARBON SOURCE-DEPENDENT TRANSCRIPTIONAL ACTIVATION OF GLUCONEOGENIC GENES BY THE REGULATORY GENE CAT8

The CSRE (carbon source-responsive element) is a sequence motif respon sible for the transcriptional activation of gluconeogenic structural g enes in Saccharomyces cerevisiae. We have isolated a regulatory gene, DIL1 (derepression of isocitrate lyase, CAT8), which is specifically r equired for derepression of CSRE-dependent genes. Expression of CAT8 i s carbon source regulated and requires a functional Cat1p (Snf1p) prot ein kinase, The derepression defect of CAT8 in a cat1 mutant could be suppressed by a mutant Mig1p repressor protein, Derepression of CAT8 a lso requires a functional HAP2 gene, suggesting a regulatory connectio n between respiratory and gluconeogenic genes. Carbon source-dependent protein-CSRE complexes detected in a gel retardation analysis with wi ld-type extracts were absent in cat8 mutant extracts, However, similar experiments with an epitope-tagged CAT8 gene product in the presence of tag-specific antibodies gave evidence against a direct binding of C at8p to the CSRE, A constitutively expressed GAL4-CAT8 fusion gene rev ealed a carbon source-dependent transcriptional activation of a UAS(GA L)-containing reporter gene, Activation mediated by Cat8p was no longe r detectable in a cat1 mutant. Thus, biosynthetic control of CAT8 as w ell as transcriptional activation by Cat8p requires a functional Cat1p protein kinase, A model proposing CAT8 as a specific activator of a t ranscription factor(s) binding to the CSRE is discussed.