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Regulation of the RNA polymerase II holoenzyme-associated cyclin-dependent kinase SRB10 Goto, Susan Lisa

Abstract

Saccharomyces cerevisiae SRB10 is a cyclin-dependent kinase associated with the RNA polymerase II holoenzyme. Although originally identified based on its role in CTD function and subsequently demonstrated to be a CTD kinase, more recent evidence has revealed another aspect of SRB10 function with respect to transcriptional regulation. SRB10 has been shown to phosphorylate several transcriptional activators involved in cellular metabolism and environmental stress responses, leading to speculation that SRB10 function is modulated in response to signals regarding the overall environmental and physiological status of the cell in order to effect appropriate levels of transcription. However, the signals and mechanisms that regulate SRB10 function are currently unknown. The goal of this research was to determine if and how SRB10 kinase activity is regulated in response to specific nutritional conditions. Data presented in this thesis demonstrate that SRB10 is negatively regulated by nitrogen limitation. In vitro kinase assays performed with SRB10 immunoprecipitated from yeast grown in nitrogen-limiting conditions revealed a transient reduction in kinase activity. In contrast, no significant effect on the in vitro kinase activity of immunoprecipitated SRB10 was observed for yeast grown in non-fermentable versus fermentable carbon sources. Down-regulation of SRB10 in response to nitrogen limitation is achieved through depletion of SRB10 protein levels, which occurs through a decrease in the stability of the SRB10 protein, representing a novel mechanism of cyclin-dependent kinase regulation.

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