Protection of genome integrity is critical for preventing genetic mutations and chromosomal rearrangements that can lead to cancer, aging-related disorders, neurological, immunological and developmental diseases, infertility, birth defects and many other disorders. DNA damage triggers the checkpoint kinases ATM and ATR to phosphorylate the C-terminus of histone H2AX in chromatin flanking DNA lesions. This phospho-H2AX, known as gamma-H2AX, serves as a signaling and protein docking platform to regulate DNA repair and cell cycle checkpoint activities. While gamma-H2AX has well known roles at DNA double- strand breaks created by ionizing radiation and other clastogens, its role at stalled or damaged replication forks during the DNA synthesis (S)-phase of the cell cycle is enigmatic. We recently discovered that gamma-HAX recruits the genome maintenance factor Brc1 to stalled or damaged replication forks. We also found that Brc1 binding to gamma-H2AX is crucial in the absence of Rqh1, which is the ortholog of human BLM DNA helicase that is mutated in Bloom's Syndrome. In this project we propose to: (1), discover why ?H2AX is crucial when Rqh1 DNA helicase is defective;(2), define and characterize the genetic deficiencies that create a critical requirement for ?H2AX and Brc1;(3), assess the functions of the electronegative surface in the BRCT5-6 interdomain linker of Brc1. The impact of these studies will be to significantly improve the understanding of how genome integrity is protected in S-phase.

Public Health Relevance

Human health depends on genome maintenance mechanisms that insure the accurate reproduction and distribution of genetic blueprints during each of the ~10,000 trillion cell divisions in the average human lifetime. These will uncover crucial insights into these mechanisms, thereby increasing the probability of developing new strategies for treating cancer and other diseases caused by genome instability.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics B Study Section (MGB)
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Reddy, Michael K
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Scripps Research Institute
La Jolla
United States
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Zhu, Min; Zhao, Hongchang; Limbo, Oliver et al. (2018) Mre11 complex links sister chromatids to promote repair of a collapsed replication fork. Proc Natl Acad Sci U S A 115:8793-8798
Zhao, Hongchang; Zhu, Min; Limbo, Oliver et al. (2018) RNase H eliminates R-loops that disrupt DNA replication but is nonessential for efficient DSB repair. EMBO Rep 19:
Ganguly, Abantika; Guo, Lan; Sun, Lingling et al. (2018) Tdp1 processes chromate-induced single-strand DNA breaks that collapse replication forks. PLoS Genet 14:e1007595
Limbo, Oliver; Yamada, Yoshiki; Russell, Paul (2018) Mre11-Rad50-dependent activity of ATM/Tel1 at DNA breaks and telomeres in the absence of Nbs1. Mol Biol Cell 29:1389-1399
Sanchez, Arancha; Gadaleta, Mariana C; Limbo, Oliver et al. (2017) Lingering single-strand breaks trigger Rad51-independent homology-directed repair of collapsed replication forks in the polynucleotide kinase/phosphatase mutant of fission yeast. PLoS Genet 13:e1007013
Reubens, Michael C; Rozenzhak, Sophie; Russell, Paul (2017) Multi-BRCT Domain Protein Brc1 Links Rhp18/Rad18 and ?H2A To Maintain Genome Stability during S Phase. Mol Cell Biol 37:
Guo, Lan; Ganguly, Abantika; Sun, Lingling et al. (2016) Global Fitness Profiling Identifies Arsenic and Cadmium Tolerance Mechanisms in Fission Yeast. G3 (Bethesda) 6:3317-3333
Jensen, Kristi L; Russell, Paul (2016) Ctp1-dependent clipping and resection of DNA double-strand breaks by Mre11 endonuclease complex are not genetically separable. Nucleic Acids Res 44:8241-9
Petersen, Janni; Russell, Paul (2016) Growth and the Environment of Schizosaccharomyces pombe. Cold Spring Harb Protoc 2016:pdb.top079764
Sánchez, Arancha; Russell, Paul (2015) Ku stabilizes replication forks in the absence of Brc1. PLoS One 10:e0126598

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