Bacterial RadA is a DnaB-type helicase interacting with RecA to promote bidirectional D-loop extension.

Homologous recombination (HR) is a central process of genome biology driven by a conserved recombinase, which catalyses the pairing of single-stranded DNA (ssDNA) with double-stranded DNA to generate a D-loop intermediate. Bacterial RadA is a conserved HR effector acting with RecA recombinase to promote ssDNA integration. The mechanism of this RadA-mediated assistance to RecA is unknown. Here, we report functional and structural analyses of RadA from the human pathogen Streptococcus pneumoniae. RadA is found to facilitate RecA-driven ssDNA recombination over long genomic distances during natural transformation. RadA is revealed as a hexameric DnaB-type helicase, which interacts with RecA to promote orientated unwinding of branched DNA molecules mimicking D-loop boundaries. These findings support a model of DNA branch migration in HR, relying on RecA-mediated loading of RadA hexamers on each strand of the recipient dsDNA in the D-loop, from which they migrate divergently to facilitate incorporation of invading ssDNA.

Citation

Léa Marie, Chiara Rapisarda, Violette Morales, Mathieu Bergé, Thomas Perry, Anne-Lise Soulet, Clémence Gruget, Han Remaut, Rémi Fronzes, Patrice Polard. Bacterial RadA is a DnaB-type helicase interacting with RecA to promote bidirectional D-loop extension. Nature communications. 2017 May 31;8:15638

PMID: 28561029

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