Endonucleases and simian virus 40 virions: origin of a virion-associated endonuclease

The origin and role of the endonuclease activity associated with purified virions of simian virus 40, previously described by this and other laboratories, have been further investigated. We found that the enzymatic activity from virions of temperature-sensitive (ts) mutants is not more heat labile than that from wild-type virions. This result was obtained for a variety of ts mutants, including three of the tsA class, and in experiments in which the enzyme was tested in both the presence and absence of viral particles. Comparison of the viron enzyme with endonucleases prepared from either serum or nuclei of uninfected cells reveals a similarity between the viron and serum enzymes based on chromatographic behavior and relative activity with different cations. Virus particles prepared free of this endonuclease were still infectious. We were unsuccessful in uncovering endonuclease in such preparations upon disruption. These data emphasize the necessity for caution in interpreting the role of particle-associated enzymes.