Strich 9513479 Cyclins are a conserved gene family that activate specific protein kinases (termed CDK's for cyclin dependent kinases). Initially, cyclins were identified as factors required for oocyte maturation and mitotic cell cycle progression. As indicated by their name, the levels of these proteins were found to oscillate during the cell cycle peaking when their activity was required. However, a rapidly emerging subclass of cyclin proteins (C-type) has been described that differs from the original groups in one important aspect. Although these proteins still activate protein kinases, their transcript levels do not vary with respect to the cell cycle. This project will investigate the yeast gene UME3, the newest member of the C-type cyclin subfamily. UME3 is required for the full repression of several meiotic genes and member of the Hsp70 heat shock super family of proteins. Since these genes are regulated in response to external stimuli, these results suggest a role for Ume3P in the adaptive response to changing environmental conditions. Consistent this hypothesis, the protein encoded UME3 (Ume3p) is rapidly destroyed when cells are exposed to heat shock, nutrient deprivation and during meiotic development. The destruction of Ume3p in response to adverse environment conditions or developmental cues represents a novel mechanism for cyclin regulation and, combined with the genetic analysis, suggest that Ume3p links the pathway that transmits exogenous signals and the transcription machinery. If correct, this system would provide the cell a rapid, flexible response to changing environmental or intracellular signals through post-translational regulation of Ume3p-dependent protein kinase activity. This study will investigate the pathway that regulates Ume3p and further elucidate the role this cyclin plays in the normal cellular response to stress. Specifically, the following questions will be addressed: 1. What are the cis and trans factors that mediate Ume3p regulation? 2. Wha t role does Ume3p play in the cellular response to stress? The long term goal of this study is to understand the underlying mechanisms by which cells translate environmental stimuli into altered gene expression programs. One critical component of this process is the connection between the signaling pathway that transmits a particular stimulus and the transcription machinery that facilitates gene expression. Such an activity would be predicted to be a regulatory molecule that can modulate gene expression directly and, itself, be regulated by external stimuli. Several findings are consistent with yeast gene Ume3p performing such a role. First, UME3 encodes a C-type cyclin. Cyclins are a conserved family of proteins that serve as molecular switches through the activation a specific protein kinases. Second, genetic analyses have revealed a role for Ume3p in negatively regulating genes involved in meiotic development or the adaptive response to stress. Third, this cyclin directly interacts with the transcriptional apparatus. Finally, Ume3p is rapidly destroyed in response to a subset of stress or differentiation signals, a novel regulatory mechanism for cyclins. These results point to the existence of a rapid, flexible system that alters gene expression in response to changing environmental signals through post-translational regulation of Ume3p-dependent protein kinase activity. This project is directed toward elucidating the pathway that regulates Ume3p and investigating the role this cyclin plays in modulating gene expression. ***
