Activation of HIV-1 enhancer sequence by vaccinia virus.

To investigate whether vaccinia virus (VV) can augment gene expression of human immunodeficiency virus type 1 (HIV-1), co-transfection experiments were carried out in which recombinant plasmids containing various portions of the HIV-1 long terminal repeat (LTR) linked to the chloramphenicol acetyltransferase (CAT) gene were transfected into cultured cells. A high level of enhancement in CAT activity directed by the HIV-1 LTRs containing the enhancer sequence was observed in cells infected with VV, as in the cells infected with type 1 herpes simplex virus (HSV-1). The sequence responsible for this augmentation of CAT activity was different from that recognized by HIV-1 Tat. These data clearly demonstrated that VV transactivates HIV-1 LTR through a mechanism distinct from that of activation by HIV-1 Tat.