Biological consequences of a reduction in the non-target DNA scanning capacity of a DNA repair enzyme.

Numerous DNA-interactive proteins have been shown to locate specific sequences within large domains of non-target DNA in vitro and in vivo by a one-dimensional diffusion mechanism; however, the biological significance of this process has not been evaluated. We have examined the biological consequences of sliding for the pyrimidine dimer-specific DNA repair enzyme T4 endonuclease V, an enzyme which scans non-target DNA both in vitro and in vivo. An endonuclease V mutant was constructed whose only altered biochemical characteristic, measured in vitro, was a loss in its ability to slide on non-target DNA. In contrast to the native enzyme, when the mutated endonuclease V was expressed in DNA repair-deficient Escherichia coli, no enhanced ultraviolet survival was conferred. These results suggest that the mechanisms which DNA-interactive proteins employ to enhance the probability of locating their target sequences are of significant biological importance.