The effects of the histone chaperone and histone modifications on nucleosome structure
Date
2016
Authors
Wang, Tao, author
Luger, Karolin, advisor
Stargell, Laurie, committee member
Yao, Tingting, committee member
Williams, Robert M., committee member
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Abstract
The nucleosome, composed of 147-bp DNA and a histone octamer, is the basic unit of chromatin in eukaryotes, which is considered as a barrier for all DNA dependent processes. Understanding how nucleosome structure is regulated provides new insights into pivotal cellular processes. Histone modifications and histone chaperones have potential roles in the regulation of nucleosome structure. Here, I investigated the role of FACT in regulating nucleosome structure. FACT (FAcilitate Chromatin Transcription) is a conserved histone chaperone that is essential for gene transcription elongation. Our biochemical data show that FACT is not only a H2A-H2B chaperone, but also a H3-H4 chaperone. By binding H3-H4, FACT facilitates tetrasome assembly. In the presence of H2A-H2B, FACT facilitates H2A-H2B deposition onto tetrasomes and hexasomes, and thus promotes nucleosome assembly. FACT is also able to tether partial nucleosome components, composed of a histone hexamer and DNA, and results in forming an unstable complex. Interaction with H2A-H2B is essential for FACT binding to tetrasomal H3-H4. In order to hold a histone hexamer, FACT also stabilizes dimer-tetramer interaction. Previous study shows that H2BK120ub facilitates FACT function in gene transcription with the help of other transcription factors. Here, we show that H2AK119ub and H2BK120ub have no effects on FACT-(H2A-H2B) interaction and FACT assembly activity. The role of select histone modifications in nucleosome structure was also determined in this dissertation. Histone modifications selected in this work are located at the entry-exit region of nucleosomal DNA. By using biochemical approaches, we find that H3Y41E (mimic phosphorylation) and H3R45E (mimic phosphorylation) affect the shape of nucleosome by facilitating nucleosomal 'DNA breathing'.
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Subject
histone
histone modification
ubiquitination
histone chaperone
fact
phosphorylation