Relationship of the cAMP-dependent protein kinase pathway to the SNF1 protein kinase and invertase expression in Saccharomyces cerevisiae.

The SNF1 protein kinase and the associated SNF4 protein are required for release of glucose repression in Saccharomyces cerevisiae. To identify functionally related proteins, we selected genes that in multicopy suppress the raffinose growth defect of snf4 mutants. Among the nine genes recovered were two genes from the cAMP-dependent protein kinase (cAPK) pathway, MSI1 and PDE2. Increased dosage of these genes partially compensates for defects in nutrient utilization and sporulation in snf1 and snf4 null mutants, but does not restore invertase expression. These results suggest that SNF1 and cAPK affect some of the same cellular responses to nutrients. To examine the role of the cAPK pathway in regulation of invertase, we assayed mutants in which the cAPK is not modulated by cAMP. Expression of invertase was regulated in response to glucose and was dependent on SNF1 function. Thus, a cAMP-responsive cAPK is dispensable for regulation of invertase.