Fig. 7.

UmuD′₂C inhibits homologous recombination facilitated by RecA. (A) Variants in plasmid pGY9738 (umuD′C wild type) were expressed in strain GW8017 (ΔumuDC). Cells harboring the variants N32A, N33A, and D34A show intermediate inhibition of RecA-mediated homologous recombination, whereas cells harboring other variants (Y11A, G52A, P54A; to the right of the vertical line) inhibit homologous recombination to a similar extent as wild-type umuD′C. Transduction efficiency is measured in CFU/PFU as a percentage of that for the empty vector (1.31 × 10⁻⁵ CFU/PFU, normalized to 100.0%): wild type, 2.09%; N32A, 58.1%; N33A, 48.4%; D34A, 38.1%; Y11A, 0.358%, G52A, 0.956%; P54A, 0.000%. (B) Homology model of UmuC (6). The backbone of UmuC is shown in yellow. UmuC loop 1 (residues 31 to 38) is shown in red, and loop 2 (residues 50 to 54) is shown in blue. UmuC residues N32, N33, and D34 (green) are near previously studied residues K342 and Y270 (purple) in the UmuC model. Previously studied residue Y11, as well as residues G52 and P54 (orange), is shown for comparison. Cells harboring variants Y270C and K342Q show a significant decrease in RecA-mediated homologous recombination. The image was prepared using VMD (28).