Effect of recB21, uvrD3, lexA101 and recF143 mutations on ultraviolet radiation sensitivity and genetic recombination in ΔuvrB strains of Escherichia coli K-12

The interaction of the recB21, uvrD3, lexA101, and recF143 mutations on UV radiation sensitization and genetic recombination was studied in isogenic strains containing all possible combinations of these mutations in a ΔuvrB genetic background. The relative UV radiation sensitivities of the multiply mutant strains in the ΔuvrB background were: recF recB lexA> recF recB uvrD lexA, recF recB uvrD>recA>recF uvrD lexA> recF recB, recF uvrD>recF lexA>recB uvrD lexA>recB uvrD> recB lexA, lexA uvrD>recB>lexA, uvrD>recF; three of these strains were more UV radiation sensitive than the uvrB recA strain. There was no correlation between the degree of radiation sensitivity and the degree of deficiency in genetic recombination. An analysis of the survival curves revealed that the recF mutation interacts synergistically with the recB, uvrD, and lexA mutations in UV radiation sensitization, while the recB, uvrD, and lexA mutations appear to interact additively with each other. We interpret these data to suggest that there are two major independent pathways for postreplication repair; one is dependent on the recF gene, and the other is dependent on the recB, uvrD, and lexA genes.