Functional domains required for tat‐induced transcriptional activation of the HIV‐1 long terminal repeat.

The transcriptional regulation of the human immunodeficiency virus (HIV) type I involves the interaction of both viral and cellular proteins. The viral protein tat is important in increasing the amount of viral steady‐state mRNA and may also play a role in regulating the translational efficiency of viral mRNA. To identify distinct functional domains of tat, oligonucleotide‐directed mutagenesis of the tat gene was performed. Point mutations of cysteine residues in three of the four Cys‐X‐X‐Cys sequences in the tat protein resulted in a marked decrease in transcriptional activation of the HIV long terminal repeat. Point mutations which altered the basic C‐domain of the protein also resulted in decreases in transcriptional activity, as did a series of mutations that repositioned either the N or C termini of the protein. Conservative mutations of other amino acids in the cysteine‐rich or basic regions and in a series of proline residues in the N terminus of the molecule resulted in minimal changes in tat activation. These results suggest that several domains of tat protein are involved in transcriptional activation with the cysteine‐rich domain being required for complete activity of the tat protein.