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EMBO Rep. 2019 May;20(5). pii: e47560. doi: 10.15252/embr.201847560. Epub 2019 Apr 4.

Shieldin - the protector of DNA ends.

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Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON, Canada.
Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON, Canada
Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada.


DNA double-strand breaks are a threat to genome integrity and cell viability. The nucleolytic processing of broken DNA ends plays a central role in dictating the repair processes that will mend these lesions. Usually, DNA end resection promotes repair by homologous recombination, whereas minimally processed ends are repaired by non-homologous end joining. Important in this process is the chromatin-binding protein 53BP1, which inhibits DNA end resection. How 53BP1 shields DNA ends from nucleases has been an enduring mystery. The recent discovery of shieldin, a four-subunit protein complex with single-stranded DNA-binding activity, illuminated a strong candidate for the ultimate effector of 53BP1-dependent end protection. Shieldin consists of REV7, a known 53BP1-pathway component, and three hitherto uncharacterized proteins: C20orf196 (SHLD1), FAM35A (SHLD2), and CTC-534A2.2 (SHLD3). Shieldin promotes many 53BP1-associated activities, such as the protection of DNA ends, non-homologous end joining, and immunoglobulin class switching. This review summarizes the identification of shieldin and the various models of shieldin action and highlights some outstanding questions requiring answers to gain a full molecular understanding of shieldin function.


DNA repair; end resection; genome stability; homologous recombination; non‐homologous end joining

[Available on 2020-05-01]

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