Date of Award
Doctor of Philosophy (PhD)
Biochemistry and Molecular Biology
College of Graduate Studies
David Thomas Long
The eggs of Xenopus laevis frogs have been used extensively to study various aspects of chromatin biology. In this document, we characterize two novel systems to study transcription (Chapter 2) and DNA double strand break repair (Chapter 4) utilizing different egg extracts. Notably, we show that nucleoplasmic extract is the first established Xenopus egg extract to support RNA polymerase II-mediated transcription of plasmid-borne gene constructs. Using this cell-free transcription system, we provide the first evidence of a molecular connection between the tumor suppressor, BRCA1, and the major epigenetic regulator, BRD4 (Chapter 3). We show BRCA1, along with its constitutive binding partner BARD1, negatively regulates the DNA-binding of BRD4. This mechanism likely involves the acetylation of histone H4K8, a known substrate for BRD4-binding, as this mark is increased in the absence of BRCA1. Furthermore, we identify and characterize a novel system for double strand break repair in extract. Importantly, we show that in this system, broken DNA ends are repaired by both non-homologous end joining as well as homologous recombination, similar to the established literature. We then use this system to show that BRD4 plays a role in homology-directed repair that is independent to its established role in transcription regulation (Chapter 4). Notably, we establish a direct interaction between BRD4 and two major DNA repair proteins, CtIP and BRG1. Loss of BRD4 results in reduced recruitment of each of these proteins to damaged DNA, and ultimately reduces DNA end resection and subsequent homologous recombination repair.
Barrows, John Kaiser, "BRCA1 and BRD4: Regulation of Chromatin Signaling in DNA Repair and Transcription" (2021). MUSC Theses and Dissertations. 608.
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