engleski

Genetic differences in postsynaptic stages of two recombinational repair pathways in Escherichia coli

Homologous recombination is an essential biological process that is involved in DNA repair and in the maintenance of genome integrity. In the bacterium Escherichia coli, homologous recombination proceeds via two genetic pathways, RecBCD and RecFOR. When operating on double- stranded DNA breaks (DSBs), the two recombination pathways differ in their initiation stages, i.e. in DNA end processing. The key role in the initiation of the RecBCD pathway is played by the RecBCD enzyme that possesses both helicase and nuclease activities. In E. coli cells deficient for RecBCD function (i.e., in recB or recC mutants), homologous recombination proceed via the RecFOR pathway, in which the activities of RecBCD protein in DNA end processing are substituted by two other enzymes, RecQ helicase and RecJ nuclease. In both pathways, the central, synaptic stage of recombination critically requires the RecA protein, while the late, postsynaptic stage is catalyzed by the RuvABC resolvase and RecG helicase. Using genetic and microscopy methods, we have studied the regulation of recombinational repair in E. coli cells exposed to gamma- irradiation. We have found that the primary role of the RecQ helicase is in the initiation of the RecF pathway and not in the resolution of recombination intermediates during the late, postsynaptic stage of recombination, as observed in eukaryotes. We have also found that the RecBCD- mediated recombinational repair of DSBs is more dependent on RuvABC and RecG proteins than the repair accomplished via RecFOR pathway, which might reflect differences in postsynaptic reactions between the two pathways.

Escherichia coli; recombinational repair; RecBCD pathway; RecFOR pathway; postsynaptic stage

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