Active displacement of RecA filaments by UvrD translocase activity

The UvrD helicase has been implicated in the disassembly of RecA nucleoprotein filaments in vivo and in vitro. We demonstrate that UvrD utilizes an active mechanism to remove RecA from the DNA. Efficient RecA removal depends on the availability of DNA binding sites for UvrD and/or the accessibility of the RecA filament ends. The removal of RecA from DNA also requires ATP hydrolysis by the UvrD helicase but not by RecA protein. The RecA-removal activity of UvrD is slowed by RecA variants with enhanced DNA-binding properties. The ATPase rate of UvrD during RecA removal is much slower than the ATPase activity of UvrD when it is functioning either as a translocase or a helicase on DNA in the absence of RecA. Thus, in this context UvrD may operate in a specialized disassembly mode.