Isolation of a cellular protein that binds to the human immunodeficiency virus Tat protein and can potentiate transactivation of the viral promoter.

The human immunodeficiency virus type 1 Tat protein is a powerful transactivator of the viral long terminal repeat (LTR). We have identified a cellular protein that strongly binds to Tat and can complement Tat transactivation in rodent cells. The cellular protein of about 36 kDa was isolated from extracts of human cells by Tat peptide-affinity chromatography and can form a complex with Tat in vitro. Tat transactivation is inefficient in rodent cells microinjected or transfected with the reporter plasmid pHIV-LTRCAT plus the Tat-expressing plasmid pCV-1. Remarkably, coinjection of purified 36-kDa protein with pHIV-LTRCAT plus pCV-1 stimulated Tat transactivation 2.7- to 4.9-fold. Taken together, our findings suggest that the 36-kDa protein may be a transcription factor or modulator that is important for efficient Tat transactivation.