The effects of lexA101, recB21, recF143 and uvrD3 mutations on liquid-holding recovery in ultraviolet-irradiated Escherichia coli K12 recA56.

Using an Escherichia coli K12 recA strain, we have tested the effects of incorporating additional mutations affecting deoxyribonucleic acid (DNA) repair on ultraviolet-radiation sensitivity and on the expression of liquid-holding recovery (LHR). (This laboratory had previously shown that a mutation at uvrA, uvrB or uvrC blocked LHR in a recA strain.) In the recA56 background, an additional lexA101 mutation had no effect on UV-radiation sensitivity or LHR. The addition of a recB21 mutation to recA56 did not alter UV-radiation sensitivity, but greatly increased the rate of LHR. The recB gene product (exonuclease V) appears to act as a competitive inhibitor both of excision repair and of photoreactivation under liquid-holding (LH) conditions. The uvrD3 mutation increased the radiation sensitivity of a recA strain, and almost completely blocked LHR. The recA uvrD strain showed more DNA degradation and DNA double-strand breaks during LH than did the recA strain. The recF143 mutation increased both UV-radiation sensitivity and LHR in a recA strain, suggesting that the recF gene product may also function in recA-independent pathways of DNA repair.