Differential suppressor effects of thessb-1 andssb-113 alleles onuvrD mutator ofEscherichia coli in DNA repair and mutagenesis

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Abstract
We have constructed double mutants carrying eithre ssb-1 or ssb-113 alleles, which encode emperature-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 allel 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 suprpessed the strong UV-sensitivity caused by the uvrD::Tn5 mutantion; (iv) in ssb-113 mutants, the level of recombination was reduced only 10-fold but 100-fold in ssb-1 mutants, showing the there was no correlation ebtween 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 allel: (vi) no addition of the spontaneous mutatior effects promoted by the uvrD::Tn5 and the ssb-113 alleles was observed. These results suggest a possible functional interactions between SSB and Helicase II in DNA repair and mutagenesis.