Effect of recB21, uvrD3, lexA101 and recF143 mutations on ultraviolet radiation sensitivity and genetic recombination in delta uvrB 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 delta uvrB genetic background. The relative UV radiation sensitivities of the multiply mutant strains in the delta uvrB background were: recF recB lexA greater than recF recB uvrD lexA, recF recB uvrD greater than recA greater than recF uvrD lexA greater than recF recB, recF uvrD greater than recF lexA greater than recB uvrD lexA greater than recB uvrD greater than recB lexA, lexA uvrD greater than recB greater than lexA, uvrD greater than 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.