Abstract
The pheromone .alpha. factor, secreted by S. cerevisiae cells of the .alpha. mating type, serves to synchronize the opposite mating type (a cells) at G1 as a prelude to fusion of the 2 cell types. In vitro, .alpha. factor inhibited the membrane-bound adenylate cyclase of these cells in a dose-dependent manner. Moreover, one class (ste5) of a cell mutants that grow normally at either 23.degree. or 34.degree. C but that are unable to respond to .alpha. factor or to mate at the higher temperature possessed an adenylate cyclase activity that was not inhibited by .alpha. factor at 34.degree. C but was fully sensitive to inhibition at 23.degree. C. Furthermore, addition of cyclic AMP to a cell culture medium shortened the period of pheromone-induced G1 arrest. Inhibition of adenylate cyclase activity by .alpha. factor may constitute, at least in part, the biochemical mode of action of the pheromone in vivo.