Abstract

The Tat protein of human immunodeficiency virus type 1 (HIV-1) is a potent trans-activator of the viral long terminal repeat (LTR). The N-terminal region of Tat is rich in proline and acidic residues analogous to the activation domains of other transcription factors such as GAL-4 and CTF/NF-1. Several basic residues are also present in this region. To investigate the role of these structural features in the Tat-mediated trans-activation, we have chemically synthesized and evaluated Tat analogs with alanine or glutamine replacing one or more of these amino acid residues. Our data show that substitution of Glu-2, His-13, or all the proline in the Pro-Xaa3-Pro triad drastically reduced activity. In contrast, changes at Arg-7, Lys-12 and any one proline residue in the triad moderately reduced, and substitution of Lys-19 showed little effect on, activity. These results show that the native structure of the N-terminal 19 amino acid sequence is essential for Tat function, and that the overall topology of this domain and not the acidic residues alone appears necessary for trans-activation.