ABSTRACT
This chapter focuses on cellular regulatory proteins that bind to the HIV-1 Long Terminal Repeat (LTR) to initiate transcription and on the viral trans-activator Tat that binds to the transactivation response region to elongate viral transcription. The 5' LTR consists of U3, R, and U5 sequences. The site of initiation of transcription is at the U3/R junction. More than a dozen proteins bind to this region. The HIV trans-activator Tat is one of the earliest viral proteins made from the integrated provirus. Functional domains of Tat have been investigated using heterologous RNA- and DNA-tethering proteins. For example, using the coat protein of bacteriophage MS2 and its operator RNA target, or Rev and its stem loop 2B from the Rev response element RNA target, the N-terminal 48 amino acids of Tat function as an independent activation domain. Tat is unique among eukaryotic transcriptional regulators in that it exerts its effects via an RNA target.
