Repeated DNA sequences in a genome represent potential sites for homologous recombination. Recombination between reiterated sequences present in different replicons may lead to their co-integration. Rhizobium sp. NGR 234 contains three replicons: the chromosome, the pSym and a megaplasmid. Based on the analysis of the sequence of the pSym (Freiberg et al. 1997) and partial sequences from the megaplasmid and the chromosome, the repeated sequence NGRRS-1 (6 kb) shared by the three replicons was identified. Co-integrations among the three replicons should be produced by homologous recombination between pairs of NGRRS-1.
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