The crystal structure of the UvsW helicase from bacteriophage T4.

In bacteriophage T4, the WXY system repairs DNA damage by a process that involves homologous recombination. This system comprises three proteins, the RecA-like recombination protein UvsX, a recombination mediator protein UvsY, and a helicase UvsW. Here we report the 2.0 A resolution crystal structure of the N-terminal two domains of the UvsW helicase (UvsWNF; residues 1-282). The structure reveals a typical helicase RecA-like domain linked to a small N-terminal alpha/beta domain that likely binds the nucleic acid substrate. The missing C-terminal portion of UvsW almost certainly corresponds to the second RecA-like domain typically found in monomeric helicases. The putative substrate binding domain is unique within the known helicase structures, and it resembles the novel "double-wing" DNA binding domain from the phage T4 MotA transcription factor that mediates the expression of T4 middle genes. The functional implications of this homology for the role of UvsW in T4 DNA metabolism are discussed.