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J Biol Chem. 2019 May 24;294(21):8606-8616. doi: 10.1074/jbc.RA119.007554. Epub 2019 Apr 11.

Slow extension of the invading DNA strand in a D-loop formed by RecA-mediated homologous recombination may enhance recognition of DNA homology.

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From the Department of Physics, Harvard University, Cambridge, Massachusetts 02138.
Department of Biology, Northeastern University, Boston, Massachusetts 02115, and.
Laboratoire de Biochimie Théorique, CNRS UMR 9080, Institut de Biologie Physico-chimique (IBPC), Paris 75005, France.
From the Department of Physics, Harvard University, Cambridge, Massachusetts 02138,


DNA recombination resulting from RecA-mediated strand exchange aided by RecBCD proteins often enables accurate repair of DNA double-strand breaks. However, the process of recombinational repair between short DNA regions of accidental similarity can lead to fatal genomic rearrangements. Previous studies have probed how effectively RecA discriminates against interactions involving a short similar sequence that is embedded in otherwise dissimilar sequences but have not yielded fully conclusive results. Here, we present results of in vitro experiments with fluorescent probes strategically located on the interacting DNA fragments used for recombination. Our findings suggest that DNA synthesis increases the stability of the recombination products. Fluorescence measurements can also probe the homology dependence of the extension of invading DNA strands in D-loops formed by RecA-mediated strand exchange. We examined the slow extension of the invading strand in a D-loop by DNA polymerase (Pol) IV and the more rapid extension by DNA polymerase LF-Bsu We found that when DNA Pol IV extends the invading strand in a D-loop formed by RecA-mediated strand exchange, the extension afforded by 82 bp of homology is significantly longer than the extension on 50 bp of homology. In contrast, the extension of the invading strand in D-loops by DNA LF-Bsu Pol is similar for intermediates with ≥50 bp of homology. These results suggest that fatal genomic rearrangements due to the recombination of small regions of accidental homology may be reduced if RecA-mediated strand exchange is immediately followed by DNA synthesis by a slow polymerase.


DNA damage; DNA polymerase; DNA recombination; RecA; cooperativity; double-strand break (DSB); fluorescence resonance energy transfer (FRET); heteroduplex formation; molecular dynamics; strand displacement synthesis

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