Interaction of Simian Virus 40 chromatin with Simian Virus 40 T-antigen.
We have studied the binding of the tumor antigen (T-antigen) of simian virus 40 to simian virus 40 chromatin (minichromosomes). The minichromosomes isolated from infected cells by a modification of standard techniques were relatively free of contaminating RNA and cellular DNA and had a ratio (by weight) of protein to DNA of approximately 1; their DNA was 50 to 60% digestible to an acid-soluble form by staphylococcal nuclease. Cleavage of this chromatin with restriction endonucleases indicated that the nuclease-resistant regions were randomly distributed in the population of minichromosomes, but were not randomly distributed within minichromosomes. Only 20 to 35% of these minichromosomes adsorbed nonspecifically to nitrocellulose filters, permitting binding studies between simian virus 40 T-antigen and chromatin to be performed. Approximately two to three times as much T-antigen was required to bind chromatin as to bind an equivalent amount of free DNA.  When T-antigen was present in excess, both chromatin and free DNA were quantitatively retained on the filters. On the other hand, when DNA or chromatin was present in excess, only one-third as much chromatin as DNA was retained. We suggest that T-antigen-chromatin complexes may be formed by the cooperative binding of T-antigen to chromatin, whereas T-antigen-DNA complexes may be formed by simple bimolecular interactions.
D000956:Antigens, Viral; D002843:Chromatin / Q000302:isolation & purification / Q000378:metabolism*; D004261:DNA Replication; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism; D013539:Simian virus 40 / Q000276:immunology; D014764:Viral Proteins / Q000302:isolation & purification / Q000378:metabolism*
D000956:Antigens, Viral; D002843:Chromatin; D004279:DNA, Viral; D014764:Viral Proteins; D004262:DNA Restriction Enzymes