Type II topoisomerase. Processively relaxes supercoiled DNA. Displays DNA-supercoiling activity only when associated with the viral histone-like protein. ATP-dependent breakage, passage and rejoining of double-stranded DNA. Binds two Mg(2+) per subunit. The magnesium ions form salt bridges with both the protein and the DNA. Can also accept other divalent metal cations, such as Mn(2+) or Ca(2+). Localizes to the cytoplasmic viral factories. Expressed in the early phase of the viral replicative cycle. Belongs to the type II topoisomerase family.