Publication Date

April 2017

Advisor(s)

Scott Holmes

Major

Molecular Biology&Biochemistry

Language

English (United States)

Abstract

The yeast cell contains 12,000 kilobasepairs of DNA. To compact this into a microscopic nucleus, organisms form chromatin, a complex consisting of DNA and organizing proteins known as histones. The histone variant H2A.Z is highly conserved across eukaryotes and possesses a variety of important functions. Loss of H2A.Z, encoded by HTZ1, in budding yeast leads to alterations in genomic integrity, including improper establishment of silencing and defects in chromosome cohesion. Previous studies in the Holmes laboratory have shown that deletion of HHO1, the gene encoding linker histone H1, suppresses silencing and growth defects observed in ?htz1 cells. In this study, I sought to further characterize the interaction between H2A.Z and H1. My results demonstrate that additional defects in ?htz1 cells can be suppressed upon deletion of HHO1. Removal of H1 suppresses a defect in plasmid retention observed in cells lacking H2A.Z, suggesting a role for these two proteins in chromosome retention. HTZ1 has a synthetic lethal relationship with 120 nonessential genes of varying function. To determine the specificity of the H1-H2A.Z interaction, I performed a screen to determine if deletion of HHO1 could suppress lethality. My results show that HHO1 deletion rescues synthetic lethal and sick phenotypes between HTZ1 and genes encoding proteins involved in ubiquitination and histone deacetylation, suggesting that these two histones function together within these processes. Removal of SWR1, the complex responsible for depositing H2A.Z at chromatin, could also suppress synthetic defects in ?htz1 cells, however this pattern of suppression was distinct from that observed from HHO1 deletion. Finally, I used chromatin immunoprecipitation to demonstrate that in the absence of H1, less H2A.Z is deposited at chromatin. I propose a model by which H1 is necessary for the proper and efficient placement of H2A.Z at chromatin by the SWR1 complex. My studies implicate a clear role for these three proteins in maintaining genomic stability.

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