The hybrid recombinational repair pathway operates in a χ activity deficient recC1004 mutant of Escherichia coli

► We studied DNA repair after UV and γ radiation, and recombination after Hfr crosses in the Escherichia coli recC1004 single mutant, recC1004 recD double mutant and their derivatives. ► We found that recD mutation supresses sensitivity to γ radiation in the recC1004 background and that DNA repair after UV and γ radiation in the recC1004 and recC1004 recD backgrounds is dependent on the recFOR and recJ gene products. In addition, DNA repair after UV and γ radiation in a recC1004 background is partially dependent on the recQ gene product. ► Different results are obtained in conjugational recombination experiments. Recombination after Hfr crosses in a recC1004 recD background is dependent on the RecJ nuclease, whereas other mutations do not show an effect on conjugational recombination in recC1004 and recC1004 recD backgrounds. ► Based on these results we emphasize the importance of recognizing the canonical χ site and 5′-exonuclease activity in the repair of DSBs.