Understanding the Functional Consequences of RNA Exosome Disease Mutations, in a Budding Yeast Model System. Public

Abstract

All cells in the human body possess the same genome, yet different cells in the body have different structure, composition, and function due to the cell-specific gene expression, which is achieved through transcriptional and post-transcriptional regulation. Ribonucleases, which are key regulators of post-transcriptional events, are conserved through evolution. One key ribonuclease machine is the RNA exosome, which is a multi-subunit 3’-5’ riboexonuclease complex. This complex, which is responsible for the processing and/or degradation of many classes of RNA, is comprised of 10-subunits, termed EXOSC proteins in humans. This core complex interacts with a variety of cofactors that are thought to confer specificity for the many different RNA targets. Recently, mutations in the genes encoding multiple RNA exosome subunits have been linked to human diseases with surprisingly different phenotypes. For example, mutations in the EXOSC2 gene cause a novel syndrome characterized by hearing loss, mild intellectual disability, and retinitis pigmentosa. In contrast, mutations in EXOSC3 cause pontocerebellar hypoplasia type 1b affecting the pons and cerebellum. How mutations in genes that encode components of the same complex cause such distinct phenotypes is not known. A potential hypothesis is that the amino acid substitution within the RNA exosome result in specific functional consequences by impacting co-factor interactions, thereby disrupting proper targeting and processing/degradation of target RNAs. My studies focus on a patient mutation, G198D, on the EXOSC2 subunit. This residue corresponds to G226 in the budding yeast orthologue of EXOSC2, Rrp4.This mutation has shown to be be temperature sensitive at 37°C, and the phenotype has been used to interaction of the RNA exosome and co-factors. The research took an exploratory approach to identify new suppressors via a High Copy Suppressor Screen, as well as a more targeted approach of overexpression of known co-factors to restore the slow growth phenotype. A genetic interaction between Rrp4 and the TRAMP complex, and the targeted screen identified Trf4 as a potential suppressor. Deletion of the TRF4 gene, showed growth defect while the rrp4-G226D cells do not show viability. The research provides insight about how amino acid changes in RNA exosome subunits alter function and cause disease.

Table of Contents

Title Page……………………………………………………………………………………………………….………………………… 1

Introduction…………………………………………………………………………………………………..…………………………..2

Materials and Methods…………………………………………………………………………………......………………………….6

Results………………………………………………………………………………………………………………………………………8

Discussion……………………………………………………………………………………………………………..………………….12

Citations………………………………………………………………………………………………………………..………………….14

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Genetics Biology, Microbiology Biology, Molecular
Mot-clé	yeast RNA Exosome
Committee Chair / Thesis Advisor	Dr. Anita H. Corbett, Emory University
Committee Members	Dr. Homa Ghalei, Emory University Dr. LaTonia Taliaferro-Smith, Emory University

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