Characterization of nuclear proteins that bind to the regulatory TGATTGGC motif in the human immunodeficiency virus type 1 long terminal repeat

We have recently elucidated the nature and function of transcription factors present in Jurkat, glial and neuronal cells that interact with modulatory region B, the nuclear receptor responsive element, in the long terminal repeat of human immunodeficiency virus type 1 (HIV-1). Considering the key role that the combination of host cell proteins plays in HIV-1 gene transcription, it appears essential to characterize proteins interacting with the adjacent region A. In vitro experiments revealed that the 5'-TGATTGGC-3'motif of region A is the target for at least three distinct proteins, one belonging to the nuclear factor I family, while two others are related to the cAMP response element binding (CREB) protein family. One of these proteins, present in DNA-protein complex C2, is formed by distinct polypeptides of relative molecular mass 43 000 and 50 000. We have purified the 43 kDa protein, which is distinct from CREB-43, and have shown that renatured p43 is able to specifically interact with site A. Transient expression experiments with vectors containing wild-type or mutant motif A revealed that basal HIV-1 gene transcription in Jurkat cells is regulated by antagonistic effects of the site A binding proteins.