Six git genes encode a glucose-induced adenylate cyclase activation pathway in the fission yeast Schizosaccharomyces pombe

An important eukaryotic signal transduction pathway involves the regulation of the effector enzyme adenylate cyclase, which produces the second messenger, cAMP. Previous genetic analyses demonstrated that glucose repression of transcription of the Schizosaccharomyces pombe fbp1 gene requires the function of adenylate cyclase, encoded by the git2 gene. As mutations in git2 and in six additional git genes are suppressed by exogenous cAMP, these ‘upstream’ git genes were proposed to act to produce a glucose-induced cAMP signal. We report here that assays of cAMP levels in wild-type and various mutant S. pombe cells, before and after exposure to glucose, show that this is the case. The data suggest that the cAMP signal results from the activation of adenylate cyclase. Therefore these ‘upstream’ git genes appear to encode a glucose-induced adenylate cyclase activation pathway. Assays of cAMP on a strain carrying a mutation in the git6 gene, which acts downstream of adenylate cyclase, indicate that git6 may function to feedback regulate adenylate cyclase activity. Thus git6 may encode a cAMP-dependent protein kinase.