UvrD Limits the Number and Intensities of RecA-Green Fluorescent Protein Structures in Escherichia coli K-12

Abstract

RecA is important for recombination, DNA repair, and SOS induction. In Escherichia coli , RecBCD, RecFOR, and RecJQ prepare DNA substrates onto which RecA binds. UvrD is a 3′-to-5′ helicase that participates in methyl-directed mismatch repair and nucleotide excision repair. uvrD deletion mutants are sensitive to UV irradiation, hypermutable, and hyper-rec. In vitro, UvrD can dissociate RecA from single-stranded DNA. Other experiments suggest that UvrD removes RecA from DNA where it promotes unproductive reactions. To test if UvrD limits the number and/or the size of RecA-DNA structures in vivo, an uvrD mutation was combined with recA-gfp . This recA allele allows the number of RecA structures and the amount of RecA at these structures to be assayed in living cells. uvrD mutants show a threefold increase in the number of RecA-GFP foci, and these foci are, on average, nearly twofold higher in relative intensity. The increased number of RecA-green fluorescent protein foci in the uvrD mutant is dependent on recF , recO , recR , recJ , and recQ . The increase in average relative intensity is dependent on recO and recQ . These data support an in vivo role for UvrD in removing RecA from the DNA.