Control of cell division in Saccharomyces cerevisiae mutants defective in adenylate cyclase and cAMP-dependent protein kinase

Abstract

Examination of the proportion of unbudded cells, terminal nuclear phenotype and DNA content of nuclei indicated that cyrl mutants of yeast defective in adenylate cyclase activity were arrested at the G1 phase of the cell cycle. The step of G1 arrest due to the cyrl mutation preceded the step sensitive to the mating pheromone. The temperature-sensitive cyrl cells did not continue growth, nor retain the capacity to conjugate at a restrictive temperature. The phenotypes of the cyrl mutant mimicked those of nutritionally limited cells. The G1 arrest caused by the cyrl mutation was overcome by the presence of a suppressor mutation, bcyl, that resulted in deficiency of a regulatory subunit of cAMP-dependent protein kinase and production of high level of cAMP-independent protein kinase. The bcyl mutation suppressed G1 arrest caused by nutritional limitation, and continued bud emergence for multiple cycles without further nuclear division. The data suggest that cAMP works as a positive effector at the start of a yeast cell cycle via activation of cAMP-dependent protein kinase.