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Updated: Aug 9, 2025

Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy
Published on: June 25, 2013
The RecA-directed recombination pathway of natural transformation initiates at chromosomal replication forks in the
Calum H G Johnston1,2, Rachel Hope1,2,3, Anne-Lise Soulet1,2
1Laboratoire de Microbiologie et Génétique Moléculaires, UMR5100, Centre de Biologie Intégrative, Centre Nationale de la Recherche Scientifique, 31062 Toulouse, France.
Abstract:
Homologous recombination (HR) is a crucial mechanism of DNA strand exchange that promotes genetic repair and diversity in all kingdoms of life. Bacterial HR is driven by the universal recombinase RecA, assisted in the early steps by dedicated mediators that promote its polymerization on single-stranded DNA (ssDNA). In bacteria, natural transformation is a prominent HR-driven mechanism of horizontal gene transfer specifically dependent on the conserved DprA recombination mediator. Transformation involves internalization of exogenous DNA as ssDNA, followed by its integration into the chromosome by RecA-directed HR. How DprA-mediated RecA filamentation on transforming ssDNA is spatiotemporally coordinated with other cellular processes remains unknown. Here, we tracked the localization of fluorescent fusions to DprA and RecA in Streptococcus pneumoniae and revealed that both accumulate in an interdependent manner with internalized ssDNA at replication forks. In addition, dynamic RecA filaments were observed emanating from replication forks, even with heterologous transforming DNA, which probably represent chromosomal homology search. In conclusion, this unveiled interaction between HR transformation and replication machineries highlights an unprecedented role for replisomes as landing pads for chromosomal access of tDNA, which would define a pivotal early HR step for its chromosomal integration.
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