trans-activation by the hepatitis B virus X protein shows cell-type specificity.

The hepatitis B virus X protein can trans-activate transcription from many viral promoters. We show here that this trans-activation is cell-type but not species specific, and that only a subset of promoters is trans-activated in any particular cell type. Furthermore, the T/t-antigens from simian virus 40 suppress this trans-activation. We hypothesize that the X protein acts via cellular factors which are phylogenetically conserved and developmentally regulated and whose effects are blocked by the T/t-antigens.