Genes encoding the regulatory (BCY1) and catalytic (TPK1, TPK2, and TPK3) subunits of the cAMP-dependent protein kinase (cAPK) are found in S. cerevisiae. bcy1- yeast strains do not respond properly to nutrient conditions. Unlike wild type, bcy1- strains do not accumulate glycogen, form spores, or become resistant to heat shock when nutrient limited. We have isolated mutant TPK genes that suppress all of the bcy1- defects. The mutant TPK genes appear to encode functionally attenuated catalytic subunits of the cAPK. bcy1- yeast strains containing the mutant TPK genes respond appropriately to nutrient conditions, even in the absence of CDC25, both RAS genes, or CYR1. Together, these genes encode the known components of the cAMP-generating machinery. The results indicate that cAMP-independent mechanisms must exist for regulating glycogen accumulation, sporulation, and the acquisition of thermotolerance in S. cerevisiae.