Activation of the vaccinia virus nicking-joining enzyme by trypsinization

The vaccinia virus nicking-joining (NJ) enzyme has been purified to homogeneity from a preparation of virus cores. The virus-specific DNA-dependent enzyme, which does not require ATP, is a single polypeptide of Mr 50,000 and possesses both endonuclease and ligase activities. The principal end product of the enzyme activity, following incubation with closed circular DNA of sufficient linking deficiency, is a linear DNA in which one of the termini has become cross-linked by the in vitro formation of a hairpin. The ability of the NJ enzyme to cross-link DNA is significantly enhanced by in vitro proteolysis. The enzymatic properties of the proteolytic digestion product, a 44-kDa polypeptide, differ in several other ways from the intact NJ enzyme. In particular, the specific activity is enhanced and the ionic strength optimum is shifted toward higher salt concentrations. It is suggested that the purified 50-kDa species is a pronuclease that is activated by proteolytic processing.