CAT5, A NEW GENE NECESSARY FOR DEREPRESSION OF GLUCONEOGENIC ENZYMES IN SACCHAROMYCES-CEREVISIAE

PCK1 encoding phosphoenolpyruvate carboxykinase is transcriptionally r egulated by two upstream activating elements, By screening for mutants that failed to derepress a UAS2(PCK1)-CYC1-lacZ reporter gene we isol ated the new recessive derepression mutation cat5. The CAT5 gene encod es a protein of 272 amino acids showing a 42% identity to the ZC395.2 gene product of Caenorhabditis elegans whose function is unknown, Dele tion of CAT5 caused a complete loss of glucose derepression affecting gluconeogenic key enzymes, Respiration, but not mitochondrial cytochro me c oxidase activity, was also affected. CAT5 expression is 5- to 6-f old repressed by glucose, and CAT5 transcriptional activation was depe ndent on CAT1 (SNF1), CAT8 and CAT5 itself. The CAT5 gene is necessary for UAS1(PCK1) and UAS2(PCK1) protein binding since a carbon source-s pecific interaction was no longer detectable in cat5 mutants, Glucose derepression of gluconeogenesis depends on the active Cat1 (Snf1) prot ein kinase and the Cat8 zinc cluster activator. Mig1p-independent over expression of CAT8 did not stimulate activation of gluconeogenic promo ters in cat1 and in cat5 mutants, Since Cat8p multicopy expression sup presses the ethanol growth deficiency in cat1 (snf1) mutants, these re sults indicate that activation of Cat8p by the Cat1p (Snf1p) kinase an d the Cat5p protein might be necessary for release from glucose repres sion.