Abstract
A protein antigenically related to the SV-40 A gene product was purified to near homogeneity from [African green monkey kidney CV-1] cells infected with the adenovirus-SV-40 hybrid virus Ad2+D2 and it contained ATPase (ATP phosphohydrolase, EC 3.6.1.3) and protein kinase (ATP:phosphotransferase, EC 2.7.1.37) activity. Both enzymatic activities co-purify with the protein through 6 stages including 1 gel filtration column, 2 ion exchange columns and a heparin affinity column. Analogous fractions from extracts of cells uninfected or infected with adenovirus 2 alone do not contain these enzymatic activities. The D2 hybrid protein resolves into 2 forms (I and II) during ion exchange chromatography. Form I, the major species (85%) of the D2 hybrid protein, elutes from DEAE-Sephadex in 0.37 M NaCl and catalyzes the hydrolysis of ATP to ADP + Pi at a rate of 3 .mu.mol/h per mg. The remaining 10-15% of the D2 hybrid protein consists of form II which elutes from DEAE-Sephadex in 0.29 M NaCl and hydrolyzes ATP and to incorporate P from ATP into either the D2 hybrid protein itself or other protein acceptors such as phosvitin. Although both forms bind DNA, the ATPase activity of form I co-sediments with SV-40 DNA more efficiently than does the protein kinase activity of form II during glycerol gradient centrifugation. The ATPase activity of form I is efficiently inhibited by addition of anti-T [tumor] .gamma.-globulin to the reaction mixture but control .gamma.-globulin has no effect. Similarly, the phosphorylation of the D2 hybrid protein by form II is inhibited by anti-T .gamma.-globulin. Phosphorylation of phosvitin is specifically inhibited by antibody only when the immune complex is removed from the reaction mixture. Thus, 1 and possibly 2 enzymatic activities are apparently carried out by the D2 hybrid protein. These findings are discussed in terms of mechanisms of SV-40 DNA replication and virally-induced transformation.