Ubiquitin-mediated Regulation of RNA Polymerase I in Saccharomyces cerevisiae

Abstract

Ribosomes are key cellular components ensuring that cells correctly synthesize their protein cohort. Dysregulation of this process can lead to improper cell growth and is linked to the progression of several types of cancers, making understanding of this process of great interest to both researchers and clinicians. Ribosome biogenesis, the process by which ribosomes are produced, is largely controlled by regulating the rate-limiting step of rDNA transcription by RNA Polymerase I, which transcribes three of the four ribosomal RNAs within the cell. Although rDNA transcription is highly regulated by post-translational modifications in response to changing environmental conditions, little is known of how RNA Polymerase I activity is regulated. Our previous research identified a novel role for ubiquitin-mediated regulation of RNA Polymerase I in ribosome biogenesis. We discovered that ubiquitination of Rpa190, the largest subunit of RNA polymerase I, regulates growth and is modulated by the deubiquitinating enzyme Ubp10. This thesis explores the details of Rpa190 ubiquitination and provides an understanding of how ubiquitination regulates rDNA transcription using both genetic and pharmacological approaches. First, it identifies how ubiquitination of Rpa190 modulates active rDNA transcription. It also identifies the SCFGrr1 complex as a potential upstream ubiquitin pathway that regulates ribosome biogenesis. Second, it identifies that the ubiquitination of Rpa190 likely serves as the physiological axis affected by the pharmacology of BMH-21, a novel small molecule being considered for use as an anti-cancer therapeutic.