Distinct effects of the UvrD helicase on topoisomerase-quinolone-DNA ternary complexes

Quinolone antibacterial drugs target both DNA gyrase (Gyr) and topoisomeras e IV (Topo IV) and form topoisomerase-quinolone-DNA ternary complexes. The formation of ternary complexes results in the inhibition of DNA replication and leads to the generation of double-strand breaks and subsequent cell de ath. Here, we have studied the consequences of collisions between the UvrD helicase and the ternary complexes formed with either Gyr, Topo IV, or a mu tant Gyr, Gyr (A59), which does not wrap the DNA strand around itself. We s how (i) that Gyr-norfloxacin (Norf)-DNA and Topo IV-Norf-DNA, but not Gyr ( A59)-Norf-DNA, ternary complexes inhibit the UvrD-catalyzed strand-displace ment activity, (ii) that a single-strand break is generated at small portio ns of the ternary complexes upon their collisions with UvrD, and (iii) that the majority of Topo IV-Norf-DNA ternary complexes become nonreversible wh en UvrD collides with the Topo IV-Norf-DNA ternary complexes, whereas the m ajority of Gyr-Norf-DNA ternary complexes remain reversible after their col lision with the UvrD helicase. These results indicated that different DNA r epair mechanisms might be involved in the repair of Gyr-Norf-DNA and Topo I V-Norf-DNA ternary complexes.