The RecA-directed recombination pathway of natural transformation initiates at chromosomal replication forks in the pneumococcus
Résumé
Natural transformation is a central horizontal gene transfer (HGT) mechanism of genome plasticity in bacteria. It relies on the capture and transport of exogenous DNA across the cell envelope, followed by its recombination at homologous chromosomal DNA sites. We investigated in Streptococcus pneumoniae the spatiotemporal choreography of the early recombination steps of transformation, coordinated by the conserved DprA protein and the general RecA recombinase on transforming DNA (tDNA). DprA and RecA accumulate in a tDNA-dependent manner at chromosomal replication forks, in a minute timescale. RecA assembles dynamic filaments at those sites, as at DNA-damaged sites during their recombinational repair. Thus, RecA-directed tDNA homology search on the chromosome appears to initiate and proceed from the replication forks in S. pneumoniae.
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