Activity of synthetic peptides from the Tat protein of human immunodeficiency virus type 1.

To determine which of the 86 amino acids in the Tat protein of human immunodeficiency virus type 1 (HIV-1) are important for transactivation, peptides from Tat were synthesized and their activity was measured in cells containing a chloramphenicol acetyltransferase reporter gene under control of the HIV long terminal repeat promoter. Although the Tat sequence contains arginine- and cysteine-rich stretches that are difficult to synthesize, it was possible to prepare pure peptides in good yield by using fluoren-9-ylmethoxycarbonyl (Fmoc) chemistry. A peptide containing residues 1-58 had 5-10% the activity of full-length Tat. Deleting 4 amino acids from the N terminus of this peptide further reduced activity, while peptides with more extensive N-terminal deletions and peptides missing the basic region at the C terminus had no detectable activity. A peptide previously reported to transactivate, Tat-(37-62), was completely inactive in our assays. Inactive peptides were also tested as possible inhibitors of transactivation. Tat-(21-38), which contains the cysteine-rich region and can form heterodimers with intact Tat in vitro, showed inhibition at high peptide concentrations. However, this effect was not specific for Tat or for the HIV promoter, since the peptide also inhibited expression from the simian virus 40 early promoter.