Dissecting the role of NuA4 and histone modifications in DNA repair to preserve genome integrity

Authors: Ahmad, Salar
Advisor: Côté, Jacques
Abstract: The eukaryotic genome is packed in the nucleus in the form of chromatin, with the nucleosome being its basic unit. The nucleosome is composed of DNA wrapped around anoctamer of histone proteins. Chromatin not only helps in the packing of DNA but also modulates various cellular functions such as transcription, replication and DNA repair. DNA damage manifests in various forms with DNA double-strand breaks (DSBs) being the most toxic which, if unrepaired, compromises genome integrity. Histones are decorated by variouspost-translational modifications that are essential for fine-tuning and regulation of chromatin.NuA4 is an acetyltransferase complex which has been well described for its role intranscription and DNA repair. Over the years, various studies have shown that NuA4 actsthrough acetylation of histones, however, new studies have highlighted non-histone targets. Our previous studies have shown how NuA4 is recruited to the site of DNA damage and howit regulates DNA repair by acetylating histones and repair proteins. Here we further dissect the role of NuA4 in DNA repair and found that it can be recruited to DSBs by an alternative mechanism relying on Lcd1ATRIP, independently of Xrs2. We also describe two new targets of NuA4 acetyltransferase activity, Nej1 and Yku80, both factors involved in repair by nonhomologous end-joining (NHEJ). In fact, we observe an antagonistic relationship between NuA4 and NHEJ factors, with acetylation of the latter favouring repair of DSBs by resection based pathways. This regulation seems evolutionary conserved with the mammalian TIP60complex antagonising pro-NHEJ factor 53BP1 (yeast Rad9) to govern the choice of repair pathway. In line with this, we further show that yeast histone H2A N-terminal tail harboursan SQ-site which is phosphorylated by Mec1ATR upon DNA damage. Our data suggests this histone mark is required to maintain the fidelity of DNA end resection by modulating the binding of Rad953BP1. We speculate that this phosphorylation acts similarly to ubiquitination of mammalian H2A tail, highlighting different histone modifications across organisms converging to achieve a similar function. Lastly, we describe the role of the YEATS domain found in the Yaf9 subunit shared by SWR1 and NuA4 complexes. We show that this domain recognizes H3K27ac and is involved in histone Htz1H2A.Z exchange, thus implicating it intranscription and DNA repair. Al together, the results presented in this thesis make important contributions to better understand the intricate roles played by NuA4 and histone modifications in the repair of DNA to maintain genome integrity
Document Type: Thèse de doctorat
Issue Date: 2021
Open Access Date: 12 July 2021
Permalink: http://hdl.handle.net/20.500.11794/69584
Grantor: Université Laval
Collection:Thèses et mémoires

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