Human-Specific Factors are Required for Tat-Mediated Trans-Activation of the HIV-1 and HIV-2 LTRs

The regulation of HIV gene expression is a complex process involving the interaction of viral regulatory gene products and host cell factors. The Tat gene has been shown to play an essential role in the positive regulation of viral gene expression (6, 9). HIV-1 Tat mediates its effect through a sequence termed TAR, which has been genetically defined to reside in the R region of the LTR (19). The TAR region is present in the leader sequence of all viral encoded RNAs, as well as both ends the proviral DNA. The boundaries of HIV-1 TAR are +1 to +80 (where +1 indicates the initiation of transcription). The TAR region has the potential to fold into a stem-loop secondary structure when transcribed into RNA.