A Schizosaccharomyces pombe gene encoding adenylate cyclase has been cloned by cross-hybridization with the Saccharomyces cerevisiae adenylate cyclase gene. The protein encoded consists of 1692 amino acids and has adenylate cyclase activity that cannot be activated by the Sa. cerevisiae RAS2 protein. Sc. pombe cyclase has a high degree of homology (approximately 60%) with the catalytic domain of Sa. cerevisiae cyclase precisely mapped by a gene-deletion analysis. A 25-40% identity is observed throughout the middle segments of approximately 1000 residues of both cyclases, large parts of which are composed of repetitions of a 23-amino acid motif similar to those found in human glycoproteins, Drosophila chaoptin, and Toll gene product. However, a segment corresponding to the NH2-terminal 620 residues of Sa. cerevisiae cyclase appears lost from Sc. pombe cyclase, and the COOH-terminal 140 residues are not well conserved between the two yeast species. Deletions involving the COOH-terminal residues of Sa. cerevisiae cyclase cause loss of activation by the RAS2 protein. These results suggest that Sc. pombe cyclase may have lost the ability to interact with RAS proteins by the loss of a regulatory site.