Differential suppressor effects of the ssb-1 and ssb-113 alleles on uvrD mutator of Escherichia coli in DNA repair and mutagenesis.

We have constructed double mutants carrying either ssb-1 or ssb-113 alleles, which encode temperature-sensitive single strand DNA binding proteins (SSB), and the uvrD::Tn5 allele causing deficiency in DNA helicase II, and have examined sensitivity to ultraviolet light (UV), recombination and spontaneous as well as UV-induced mutagenesis. We have found in a recA+ background that (i) none of the ssb uvrD double mutants was more sensitive to UV than either single mutant; (ii) the ssb-1 allele partially suppressed the strong UV sensitivity of uvrD::Tn5 mutants; (iii) in the recA730 background with constitutive SOS expression, the ssb-1 and ssb-113 alleles suppressed the strong UV-sensitivity caused by the uvrD::Tn5 mutation; (iv) in ssb-113 mutants, the level of recombination was reduced only 10-fold but 100-fold in ssb-1 mutants, showing that there was no correlation between the DNA repair deficiency and the recombination deficiency; (v) the hyper-recombination phenotype of the uvrD::Tn5 mutant was suppressed by the addition of either the ssb-1 or the ssb-113 allele; (vi) no addition of the spontaneous mutator effects promoted by the uvrD::Tn5 and the ssb-113 alleles was observed. These results suggest a possible functional interaction between SSB and Helicase II in DNA repair and mutagenesis.