Main steps in DNA double-strand break repair: an introduction to homologous recombination and related processes

Abstract

DNA double-strand breaks arise accidentally upon exposure of DNA to radiation and chemicals or result from faulty DNA metabolic processes. DNA breaks can also be introduced in a programmed manner, such as during the maturation of the immune system, meiosis, or cancer chemo- or radiotherapy. Cells have developed a variety of repair pathways, which are fine-tuned to the specific needs of a cell. Accordingly, vegetative cells employ mechanisms that restore the integrity of broken DNA with the highest efficiency at the lowest cost of mutagenesis. In contrast, meiotic cells or developing lymphocytes exploit DNA breakage to generate diversity. Here, we review the main pathways of eukaryotic DNA double-strand break repair with the focus on homologous recombination and its various subpathways. We highlight the differences between homologous recombination and end-joining mechanisms including non-homologous end-joining and microhomology-mediated end-joining and offer insights into how these pathways are regulated. Finally, we introduce noncanonical functions of the recombination proteins, in particular during DNA replication stress.

NBS1 promotes the endonuclease activity of the MRE11‐RAD50 complex by sensing CtIP phosphorylation

“…While unrepaired DSBs may result in cell death, their inaccurate repair can lead to mutagenesis and inappropriate chromosomal translocations (Ranjha et al, 2018). DNA doublestrand breaks (DSBs) are difficult to repair due to the loss of genetic information in both DNA strands.…”

“…DNA doublestrand breaks (DSBs) are difficult to repair due to the loss of genetic information in both DNA strands. The sister chromatid serves as an HR template in most cases in vegetative cells, explaining why recombination can only function in the cell cycle phases when sister chromatids are available (Ranjha et al, 2018). Cells possess two main mechanisms for DSB repair.…”

“…Cells possess two main mechanisms for DSB repair. The decision whether and to which extent to resect DNA ends therefore regulates the pathway choice in DSB repair (Ranjha et al, 2018). The second mechanism is template-dependent homologous recombination (HR), which is generally restricted to the S-G2 phase of the cell cycle.…”

DNA entry, exit and second DNA capture by cohesin: insights from biochemical experiments

“…DSBs are the most deleterious form of DNA damage and are repaired by homologous recombination using, in most cases, a stretch of intact homologous DNA on the sister chromatid as a template [74]. The Mre11 nuclease, as part of the MRN complex, is the first detector of DSBs and initiates DNA resection in coordination with the actions of other nucleases and helicases, creating ssDNA overhangs at DSB sites [74]. This ssDNA region serves as a loading platform for the Rad51 recombinase to initiate homologous paring of the ssDNA and intact dsDNA template, which is followed by DNA synthesis [75].…”

Variation in RAD51 details a hub of functions: opportunities to advance cancer diagnosis and therapy

“…A key intermediate in the complex choreography of the DNA strands underlying HR is single-stranded DNA (ssDNA), generated near the lesion, bound by RAD51 protein. Initial nucleation of RAD51 on the ssDNA is followed by binding of additional protomers, resulting in a dynamic nucleoprotein filament with homology search and DNA strand exchange capabilities 2 . The product of the breast cancer–associated gene 2 ( BRCA2 ) acts as a molecular scaffold (mediator) in this process by chaperoning RAD51 onto replication protein A (RPA)-coated ssDNA 3 .…”