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Homology recognition without double-stranded DNA-strand separation in D-loop formation by RecA
Takehiko Shibata1,2,3, Shukuko Ikawa3, Wakana Iwasaki4
1Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami Ohsawa, Hachioji, Tokyo 192-0397, Japan.
Nucleic Acids Research
|January 12, 2024
Summary
RecA/Rad51 protein facilitates DNA repair by catalyzing D-loop formation. Contrary to prior models, double-stranded DNA recognizes homologous single-stranded DNA before strand separation, with aromatic residues crucial for later processing steps.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Homologous recombination and DNA repair are vital cellular processes.
- RecA/Rad51 proteins are central to these processes, catalyzing D-loop formation.
- The mechanism of double-stranded DNA (dsDNA) recognizing homologous single-stranded DNA (ssDNA) remains debated.
Purpose of the Study:
- To investigate the role of aromatic residues in the RecA/Rad51 β-hairpin loop (L2) during DNA homology search.
- To elucidate the sequence of events in D-loop formation, specifically the timing of dsDNA strand separation relative to homology recognition.
Main Methods:
- Experimental testing of a model involving aromatic residue-mediated dsDNA strand separation prior to homology recognition.
- Analysis of the necessity of the aromatic residue for homology recognition versus D-loop processing.
Main Results:
- The aromatic residue at the tip of the β-hairpin loop (L2) is not essential for homology recognition.
- This aromatic residue is required for subsequent D-loop processing.
- dsDNA does not unwind during the homology search but only after homologous ssDNA is recognized.
Conclusions:
- dsDNA recognizes its homologous ssDNA prior to strand separation.
- This recognition mechanism, without immediate dsDNA unwinding, minimizes DNA stress, facilitating homology-dependent functions in vivo and in vitro.
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