Date of Award
Doctor of Philosophy (PhD)
DNA double strand breaks represent deleterious lesions which can either be caused by environmental or endogenous sources of DNA damage. Efficient DNA damage response which ensures repair of these lesions is therefore critical for maintenance of genomic stability. The repair happens in the context of chromatin, a three-dimensional nucleoprotein complex consisting of DNA, histones and associated proteins. As such, mechanisms that modulate chromatin structure, many of which involve the histone component of chromatin, have been shown to play a role in regulation of the DNA damage response. In my thesis work I characterize two conserved histone H2A functional domains that are required for normal response to DNA damage. In the first part of my thesis, my collaborators and I demonstrate that Tetrahymena major histone H2A.S contains an H2A.X variant-specific SQ motif within its C-terminal tail, providing the first description of this region in ciliated protozoa. The function of the SQ motif is mediated by post-translational phosphorylation of the conserved serine which is essential for normal progression through Tetrahymena life cycle, and in particular, meiosis. This study provides the first evidence for the existence of meiotic DSBs in Tetrahymena and defines the time interval of meiotic recombination in this organism. In the second part of my thesis, I describe a functional domain which encodes a unique and previously unrecognized role for the histone H2A Nterminal tail in the DNA damage response in S. cerevisiae. A DNA damage survival property exists within the conserved SRS motif spanning residues 17-19 of a single turn α-helical region in the H2A tail, known as the ‘knuckle’. I demonstrate that the SRS motif is required for efficient checkpoint recovery following successful repair, a function independent of post-translational modifications. Another contribution of histone H2A in S. cerevisiae, specific to the MMS induced DNA damage response, is provided by the three amino-terminal lysines which appear to be functionally redundant. My collaborators and I demonstrate that in vivo two of the lysines, H2A K4 and H2A K7, are acetylated individually as well as together , and identify the third lysine, H2A K13, as a novel acetylation site in S. cerevisiae.
Gjoneska, Elizabeta, "Characterization of Histone H2A Functional Domains Important for Regulation of the DNA Damage Response" (2010). Student Theses and Dissertations. 267.