Chrysodeixis chalcites nucleopolyhedrovirus encodes an active DNA photolyase

UV-radiation induces two types of lesions in DNA: cyclobutane pyrimidine dimers [CPD] and (6-4) photoproducts. These lesions can be repaired by specific DNA photolyases, which occur in all organisms except placental mammals. DNA photolyases are active under the influence of blue light. On the basis of amino acid homology two classes of CPD photolyases can be distinguished. Recently, class II CPD photolyase (phr) genes have been identified in plusiine-infecting group II nucleopolyhedroviruses (NPVs). In the Chrysodeixis chalcites NPV genome two putative phr genes are present. Expression of Cc-phr2, but not Cc-phr1, was able to complement a photolyase deficiency in Escherichia coli, indicating that Cc-phr2 encodes an active photolyase. To further characterize this photolyase, Cc-phr2 was overexpressed in E. coli and the resulting photolyase was purified. Spectral measurements indicated the presence of FAD as co-factor, but a second chromophore appeared to be absent. In vitro, recombinant Cc-phr2 photolyase specifically bound F0 (8-hydroxy-7,8-didemethyl-5-deazariboflavin), a rare antenna chromophore in eukaryotes. After reconstitution of the photolyase, FAD and F0 were present in approximately equimolar amounts. The F0 chromophore is functionally active in reconstituted Cc-phr2 photolyase as judged from the increase in the in vitro DNA repair activity. This study demonstrates for the first time that a functional photolyase is encoded by an insect virus and this may have implications for baculovirus applications in insect biocontrol.