Site-directed mutagenesis of the Saccharomyces cerevisiae CDC25 gene: effects on mitotic growth and cAMP signalling.

A potential membrane-interacting site within the essential growth-controlling carboxy-terminal region of the CDC25 protein was interrupted by a lethal mutation (1461 Tyr----Asp and 1462 Leu----Arg). The elimination of two potential phosphorylation sites found in the same region (1489 Thr----Pro and 1584 Ser----Pro) does not affect growth but completely prevents glucose-induced cAMP signalling in the double mutant, whereas the single mutants produce normal or slightly retarded cAMP signals. A cluster of five potential targets for cAMP-dependent phosphorylation at the amino-terminal region could be deleted without affecting phenotypic properties. It is concluded that the carboxy-terminal 137 residues of the CDC25 protein are involved in three different functions: control of mitotic growth, glucose-induced hyperactivation of adenylate cyclase, and feed-back inhibition of cAMP synthesis.