Publication Date

April 2019

Advisor(s)

Scott Holmes

Major

Molecular Biology&Biochemistry

Language

English (United States)

Abstract

Histones are proteins that form a complex with DNA to compact it into chromatin. Chromatin structure, in turn, controls gene expression. Four histones, H2A, H2B, H3 and H4, form the nucleosome core complex around which DNA loops. The fifth histone, H1 is a linker histone which compacts chromatin further. Previous research in the Holmes lab suggests that H1 and the variant histone H2A.Z interact to foster genome stability in Saccharomyces cerevisiae. In the absence of H2A.Z, abnormal phenotypes are observed; however, when H1 is also absent from the cell, the deleterious phenotypes of H2A.Z are suppressed. This study aims to investigate the specifics of the interaction between H1 and H2A.Z by identifying cellular processes in which they are interacting. Further, the study investigates a previously identified pathway involved in histone tail ubiquitination and methylation, the Rad6-Bre1 pathway, to specify H1 and H2A.Z’s role in this cellular process. Through a recall to life assay, it was concluded that H1 and H2A.Z are important for processes involving nucleosome stability in relation to transcriptional induction and elongation, histone acetylation, histone deacetylation and DNA damage response. Further, in investigating the relationship between H1 and H2A.Z with the Rad6-Bre1 pathway through a plasmid shuffle experiment, it was concluded that H2A.Z has a synthetic lethal relationship with mutants that cannot methylate H3 at lysine 4 while it does not have a defect with mutants that cannot methylate H3 at lysine 79. Further, H2A.Z has a synthetic sick relationship with mutants that cannot ubiquitinate H2B at lysine 123, a prerequisite step for the methylation of H3 at K4 and K79. A subsequent deletion of HHO1 does not suppress these defects suggesting that H1 is not directly involved in the modifications introduced by Rad6-Bre1 and downstream elements of this pathway but interacts with Rad6-Bre1 and H2A.Z in an independent fashion. This project more broadly adds to our knowledge of chromatin structure, function and dynamics. Further, these processes and interactions between histones and other pathways are conserved across eukaryotes; as a result, the findings of this project can be directly translatable to higher-order organisms.

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