Characterization of a DNA topoisomerase encoded by Amsacta moore entomopoxvirus

We have identified an Amsacta moorei entomopoxvirus (AmEPV) gene encoding a DNA topoisomerase. The 333-amino acid AmEPV topoisomerase displays instructive sequence similarities to the previously identified topoisomerases encoded by five genera of vertebrate poxviruses. One hundred nine amino acids are identical or conserved among the six proteins. The gene encoding AmEPV topoisomerase was expressed in bacteria and the recombinant enzyme was partially purified. AmEPV topoisomerase is a monomeric enzyme that catalyzes the relaxation of supercoiled DNA. Like the vaccinia, Shope fibroma virus, and Orf virus enzymes, the AmEPV topoisomerase forms a covalent adduct with duplex DNA at the target sequence CCCTT decreases. The kinetic and equilibrium parameters of the DNA cleavage reaction of AmEPV topoisomerase (Kobs = 0.08 sec-1; Kcl = 0.22) are similar to those of the vaccinia virus enzyme.