Introduction of superhelical turns into DNA by adenoviral core proteins and chromatin assembly factors

The interaction in vitro between adenoviral histone-like proteins and DNA in the presence of chromatin assembly factors was investigated. Viral core protein VII or its precursor pVII was incubated with DNA in the presence of an extract of HeLa cell chromatin, which mediates nucleosome assembly from histones and DNA. We have demonstrated that either protein can introduce superhelical turns into relaxed closed-circular DNA and that the presence of chromatin extract is necessary for the supertwisting effect. A greater density of superhelical turns was produced by pVII than by VII, but neither protein-DNA interaction resulted in the "physiological" amount of supertwisting produced by histones. The inhibition of histone-induced supercoiling by both proteins and the protection of turns in supertwisted starting material are also described. The nucleosome assembly factor, nucleoplasmin, fails to mediate the introduction of superhelical turns by VII or pVII.