Endonuclease activity associated with purified simian virus 40 virions

Purified simian virus 40 has associated with it an endonuclease activity which converts form I (double-stranded, circular) simian virus 40 deoxyribonucleic acid to a nicked form that sediments as a homogeneous peak in alkaline sucrose gradients. The enzyme is dependent on magnesium ions for activity and is completely inhibited by ethylenediaminetetraacetic acid (0.02 m) or heat (80 C for 10 min). In tris(hydroxymethyl)aminomethane-hydrochloride buffer it exhibits optimal activity between pH 6.7 and 7.1 at 37 C. Gel electrophoretic analysis of purified, disrupted virus indicates the absence of detectable host cell protein contamination.