Bre1-dependent H2B ubiquitination promotes homologous recombination by stimulating histone eviction at DNA breaks.

Sihao Zheng,Guangxue Liu,Dan Li,Min Wang,Jingyao Li,Simin Zhang,Yang Dong,Zhen Lu,Haoyang Peng,Guohong Li,Poyuan Xing,Meng Wang,Grzegorz Ira,Xuefeng Chen,Xuejie Wang

doi:10.1093/nar/gky918

Abstract

Repair of DNA double-strand breaks (DSBs) requires eviction of the histones around DNA breaks to allow the loading of numerous repair and checkpoint proteins. However, the mechanism and regulation of this process remain poorly understood. Here, we show that histone H2B ubiquitination (uH2B) promotes histone eviction at DSBs independent of resection or ATP-dependent chromatin remodelers. Cells lacking uH2B or its E3 ubiquitin ligase Bre1 exhibit hyper-resection due to the loss of H3K79 methylation that recruits Rad9, a known negative regulator of resection. Unexpectedly, despite excessive single-strand DNA being produced, bre1Δ cells show defective RPA and Rad51 recruitment and impaired repair by homologous recombination and response to DNA damage. The HR defect in bre1Δ cells correlates with impaired histone loss at DSBs and can be largely rescued by depletion of CAF-1, a histone chaperone depositing histones H3-H4. Overexpression of Rad51 stimulates histone eviction and partially suppresses the recombination defects of bre1Δ mutant. Thus, we propose that Bre1 mediated-uH2B promotes DSB repair through facilitating histone eviction and subsequent loading of repair proteins.

Highlights

DNA repair is crucial for faithful transmission of genetic information into daughter cells
Previous genetic studies suggested that the E3 ubiquitin ligase Bre1 is required for proper resistance to ionizing radiation (IR) in yeast [45]
Upon CPT, methyl methanesulfonate (MMS) or HU treatment, K123R cells exhibited a similar resistance profile as observed in bre1Δ or bre1ΔK123R mutants (Supplementary Figure S8). These results demonstrate that the functions of Bre1 in DNA damage response, resection and repair by homologous recombination (HR) are executed through controlling H2B-K123 ubiquitination

Summary

Introduction

DNA repair is crucial for faithful transmission of genetic information into daughter cells. DNA double-strand breaks (DSBs) are potent cytotoxic DNA lesion challenging genome stability that must be repaired faithfully to prevent cell death or tumorigenesis [1,2]. DSBs can be repaired by either homologous recombination (HR) or nonhomologous end joining (NHEJ), and the choice between these two pathways is regulated by the cell cycle [3,4]. HR is the dominant repair pathway in S and G2 phases. It requires a homologous template to direct the repair and is considered to be more accurate [3,4]. NHEJ operates predominantly in the G1 phase when sister chromatids are not available for repair. NHEJ is less accurate as it can lead to small insertion or deletions at DSBs [3,4]

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Conclusion