Transcriptional regulation and ubiquitin-mediated proteolysis are two processes that feature prominently in the control of cell growth and development. Consistent with their pivotal roles in maintaining cellular homeostasis, deregulation of both transcription and ubiquitin-mediated protein destruction lies at the heart of a variety of human diseases, including cancer. At first blush, these two processes have apparently very little in common-transcription is the first step in the life of any protein;proteolysis is the last. Despite the disparate nature of these processes, however, a growing body of evidence suggests that components of the ubiquitin-proteasome system are directly involved in the regulation of gene expression. The connection of these processes reveals a previously unanticipated level of transcriptional control that we are anxious to explore. This proposal defines a research strategy to investigate how ubiquitin-dependent processes regulate the activity of three key players in transcriptional regulation-transcriptional activators, RNA polymerase, and histones. These studies will be complemented with a highly-integrated analysis of the role of proteasome components in gene activation. To achieve this objective, we will employ a combination of genetic and biochemical approaches using the model organism Saccharomyces cerevisiae. We will study how ubiquitylation of the prototypical yeast activator Gal4 connects transcriptional activation to events required for co-transcriptional pre-messenger RNA processing. We will investigate how ubiquitylation of the largest subunit of RNA polymerase II regulates polymerase activity and subunit composition, and how ubiquitylation of histone H2B modulates histone dynamics and interaction of chromatin with the nuclear environment. And, finally, we will study how proteasome subunits are recruited to chromatin and their function in both gene activation and transcriptional silencing. Results of these studies will provide valuable insight into how transcription and the ubiquitin-proteasome systems intersect, and will serve as a paradigm for our understanding of this new dimension in transcriptional control. Importantly, our work will also provide an intellectual framework for understanding how these processes contribute to human disease, and offers the potential to identify ways to regulate aberrant transcription by modulating the activity of the ubiquitin system;a strategy that could very-well form the basis of improved cancer therapies.
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