trans-activation of viral enhancers including long terminal repeat of the human immunodeficiency virus by the hepatitis B virus X protein.

Human hepatitis B virus contains an open reading frame designated X. We have investigated the trans-activating function of the hepatitis B virus X gene in regulating transcriptional control elements. In the HBV genome the major target for X trans-activation is the enhancer element. Further, the X protein stimulates several other viral promoters/enhancers including the long terminal repeats (LTR) of human retroviruses. One of the viral sequences studied in detail is the human immunodeficiency viral (HIV) LTR which is trans-activated by the X protein. Using mutational analysis of the HIV LTR, we show that the NF-kappa B sequences contained within the U3 region are involved in this stimulatory activity. Nuclear run-on analyses support the notion that X-mediated trans-activation occurs at the level of transcription.