Identifying Subunit Organization and Function of the Nuclear RNA Exosome Machinery

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Losh, Jillian; <p></p>
RNA exosome; RNA processing; RNA degradation; snoRNA; pontocerebellar hypoplasia type 1b; EXOSC3; TRAMP complex; Medicine and Health Sciences
thesis / dissertation description
IDENTIFYING SUBUNIT ORGANIZATION AND FUNCTION OF THE NUCLEAR RNA EXOSOME MACHINERY Jillian Strother Losh, A.S., B.S. The eukaryotic RNA exosome processes and degrades many classes of RNA. It is present in the nucleus and the cytoplasm, highly evolutionarily conserved, and essential for viability. Since the RNA exosome is such a significant component of the RNA degradation machinery, it is unsurprising that even single point mutations in a few of its subunits have been linked to human disease. For example, at least eight point mutations in a single subunit of the RNA exosome have been linked to pontocerebellar hypoplasia subtype 1b (PCH1b). My work has included the development of a laboratory model system to assess the specific effects of these mutations on the structure and function of the RNA exosome. My collaborators and I have employed the common model organism Saccharomyces cerevisiae for this work since both the RNA exosome and other components of RNA degradation machinery are conserved throughout eukaryotes. Our research has shown that at least one PCH1b-associated mutation negatively affects the stability of the RNA exosome, although it remains functional. The effect of this mutation is conserved between yeast and mouse cells.The RNA exosome requires various cofactors in both the nucleus and the cytoplasm for substrate delivery. The other half of my work focuses on a nuclear cofactor of the RNA exosome, the TRAMP complex. This complex is comprised of an RNA helicase and a poly(A) polymerase, as well as an RNA-binding subunit. However, it is currently unclear how the TRAMP complex is specifically assembled and moreover, if it is essential for life. The poly(A) polymerase subunit consists of a catalytic domain, as well as disordered regions that are required for protein interactions. My work has shown that the catalytic core of the TRAMP complex is necessary and sufficient for its essential functions, although a specific interaction between the two enzymatic subunits is required for snoRNA biogenesis and possibly other cellular functions. These and future studies will help define the role of the TRAMP complex in the RNA degradation process and determine its importance for cellular viability.