The long term goal of the proposed research is to identify and understand the components of the regulatory apparatus that governs cell cycle initiation. Utilizing budding yeast as an experimental system that is tractable to genetic, biochemical and cell biological approaches, we have identified and partially characterized a novel family of proteins known as the G1 cyclins encoded by the genes CLN1, CLN2 and CLN3.
The specific aims of this proposal are to: 1. To characterize the state of modification of G1 cyclins and their relationship to stability and function. We propose to characterize the nature and the sites of covalent modification of the Cln1 and Cln2 proteins in vegetative cells and under conditions known to regulate G1 cyclin function and cell cycle progression. Both genetic and biochemical approaches will be used to assign specific functions to these modifications. 2. To characterize the mechanisms governing G1 cyclin activity and abundance. Our previous studies have established that the stimuli known to regulate cell cycle progression during G1 in yeast regulate the abundance of G1 cyclins at both the transcriptional and the post- transcriptional levels. Using combined biochemical and genetic approaches, we will analyze the mechanisms of post-transcriptional regulation of Cln1 and Cln2 both during the cell cycle and in response to mating pheromone and nutrient limitation. Transcriptional regulation of these genes are currently being investigated under another research grant (P01GM46OO6). 3. To characterize new components of the regulatory apparatus governing G1 cyclin activity and abundance. We will identify new components of the G1 cyclin regulatory apparatus by isolating extragenic mutants that affect the ability of cells to regulate CLN function in response to environmental regulators of cell cycle progression. We will then characterize those genes and their products with the ultimate goal of reconstructing the mechanisms by which signal transduction pathways interface with the cell cycle regulatory machinery. Accomplishing these goals will contribute to our understanding of the mechanisms by which normal cells regulate proliferation and provide a framework to approach the problem of neoplasia.
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