[Existence of a form of SV40 T antigen incapable of interacting with DNA].

The interaction of SV40 T-antigen and viral DNA was studied by using adsorption of DNA-protein complexes on nitrocellulose filters. The T-antigen purification procedure included ion-exchange chromatography on DEAE-cellulose, selective adsorption of cellular proteins on single-stranded DNA-cellulose, chromatography on heparin-Sepharose and removal of cell proteins by an immunosorbent. Only the latter step allowed to remove the contamination of cellular DNA-binding proteins, judging from the reaction of T-antigen neutralization by specific antibodies. It was shown that T-antigen and cellular DNA-binding proteins interact with SV40 DNA at different values of pH, namely ah 6,0-6,4 and 7,9, respectively. The T-antigen obtained was passed through a column with native DNA-cellulose at pH and ionic strength values optimal for interaction with DNA. The bulk of T-antigen (30-40%) did not bind to native thymus DNA and did not interact with SV40 DNA. It is assumed that this fraction is a form of T-antigen, which undergoes structural or functional changes during specific interaction with viral or cellular DNAs.