Different effects of recJ and recN mutations on the postreplication repair of UV-damaged DNA in Escherichia coli K-12

Two mutations known to affect recombination in a recB recC sbcBC strain, recJ284::Tn10 and recN262, were examined for their effects on the postreplication repair of UV-damaged DNA. The recJ mutation did not affect the UV radiation sensitivity of uvrB and uvrB recF cells, but it increased the sensitivity of uvrB recN (∼ 3-fold) and uvrB recB (∼ 8-fold) cells. On the other hand, the recN mutation did not affect the UV sensitivity of uvrB recB cells, but it increased the sensitivity of uvrB (∼ 1.5-fold) and uvrB recF (∼ 4-fold) cells. DNA repair studies indicated that the recN mutation produced a partial deficiency in the postreplication repair of DNA double-strand breaks that arise from unrepaired daughter strand gaps, while the recJ mutation produced a deficiency in the repair of daughter strand gaps in uvrB recB cells (but not in uvrB cells) and a deficiency in the repair of both daughter strand gaps and double-strand breaks in uvrA recB recC sbcBC cells. Together, these results indicate that the recJ and recN genes are involved in different aspects of postreplication repair