The rye mutants identify a role for Ssn/Srb proteins of the RNA polymeraseII holoenzyme during stationary phase entry in Saccharomyces cerevisiae

Saccharomyces cerevisiae cells enter into a distinct resting state, known a s stationary phase, in response to specific types of nutrient deprivation. We have identified a collection of mutants that exhibited a defective trans criptional response to nutrient limitation and failed to enter into a norma l stationary phase. These rye mutants were isolated on the basis of defects : in the regulation of YGP1 expression. In wild-type cells, YGP1 levels inc reased during the growth arrest caused by nutrient deprivation or inactivat ion of the Ras signaling pathway. In contrast, the levels of YGP1 and relat ed genes were significantly elevated in the,rye mutants during log phase gr owth. The rye defects were not specific to this YGP1 response as these muta nts also exhibited multiple defects in stationary phase properties, includi ng an inability to survive periods of prolonged starvation. These data indi cated that tho RYE genes might encode important regulators of yeast cell gr owth. Interestingly, three of the RYE genes encoded the Ssn/Srb proteins, S rb9p, Srb10p, and Srb11p, which ale associated with the RNA polymerase II h oloenzyme. Thus, the RNA polymerase II holoenzyme may be a target of the si gnaling pathway is responsible for coordinating yeast cell growth with nutr ient availability.