Mutations in the yeast gene A RDl lead to inability to respond to a-factor, inability to enter stationary phase, and inability to sporulate, suggesting an important role for the ARD7 gene product in controlling the switch between the mitotic cell cycle and alternative cell fates. MATa, ardl cells seem to be defective in the expression of all a-specific functions, whereas MATa, ardl cells respond normally to a-factor. We propose that ARDI is required for the expression of genes involved in a-mating functions, stationary phase, and sporulatlon. The A RDT gene has been cloned and sequenced; there is weak homology between the C terminus of the ARD7 protein, the C-terminal region of MATa2, and the homeo box.