Possible nuclease activity of the T-antigen of virus SV-40

A preparation of the T-antigen of virus SV-40 was isolated from an extract of golden hamster tumors by precipitation with ammonium sulfate followed by fractionation on DEAE-cellulose. Despite 100-fold purification of the preparation it contained traces of cell proteins as impurities. Treatment of calf thymus DNA with the preparation of T-antigen in the presence of magnesium ions considerably reduced the viscosity of the DNA solution during the first hour of incubation. The T-antigen, if inactivated by heating, or the analogous fraction from normal hamster tissues had no such action. During centirfugation in a sucrose gradient the sedimentation constant of hamster DNA was reduced after treatment with T-antigen from 28 S to 16 S, corresponding to a reduction of about 4–5 times in the molecular weight of the DNA. It can be concluded from these results that the partially purified preparation of T-antigen of virus SV-40 possesses endonuclease activity.