Yeast cdc35 mutants are defective in adenylate cyclase and are allelic with cyr1 mutants while CAS1, a new gene, is involved in the regulation of adenylate cyclase.

Newly isolated temperature-sensitive cdc35 mutants of Saccharomyces cerevisiae have been characterized. They show the morphology, growth and conjugation characteristics typical of class-A or class-II start mutants. The cdc35 mutation induces a significant decrease of the intracellular cAMP level and produces a thermolabile adenylate cyclase. By classical genetic criteria the CDC35 gene is identical with the structural gene of adenylate cyclase, CYR1. The results of the mutant selection, the kinetics of macromolecule accumulation and the cell-density change of cdc35 mutants at the restrictive temperature, indicate that CDC35 function may not be cell cycle-specific. A new mutation, cas1, was isolated and partially characterized. It mediates the suppression by external cAMP of the unlinked cdc35 mutation. It causes a slight increase of the intracellular cAMP level and has strong effects on the adenylate cyclase activities, especially on the Mg2+ dependent activity. The data suggest that the CAS1 protein is a controlling element of adenylated cyclase. The CAS1 locus is different from the RAS1 and RAS2 loci.