We have isolated 16 independent Schizosaccharomyces pombe cDNA clones that suppress the temperature-sensitive (ts) phenotype of a Saccharomyces cerevisiae strain containing the dominant-negative RAS2val19ala22 allele. Fourteen of these cDNAs encode Sz. pombe Ras1. The other two clones encode the C-terminal region of a protein we have named Pka1. We have cloned the pka1 gene from a Sz. pombe genomic library. It contains an uninterrupted open reading frame encoding a 512-amino-acid (aa) protein. The C-terminal region (aa 200-512) of Pka1 is 51-63% identical to cAMP-dependent protein kinase (Pka) catalytic subunits from other eukaryotes. Production of Pka1 suppresses the ts phenotypes exhibited by Sa. cerevisiae ras1-ras2ts or cyr1ts strains. Furthermore, overproduction of Pka1 in Sz. pombe results in a sterile phenotype and an abnormal morphology similar to that exhibited by cells in which the cAMP pathway is constitutively activated. These observations suggest that pka1 encodes the Sz. pombe Pka catalytic subunit.