Structural arrangements of transcription control domains within the 5'-untranslated leader regions of the HIV-1 and HIV-2 promoters

Promoter-proximal downstream regions of the human immunodeficiency viruses (HIV-1 and HIV-2) mediate the action of the viral transcription activator protein, Tat. We demonstrate here that the downstream domain of each virus interacts with two RNA polymerase II transcription factors. One of these, CTF/NF I, is a multifunctional protein associated previously with activation of transcription and DNA replication. The other cellular protein, designated LBP-1 (leader-binding protein-1), recognizes repeated elements within an extended region of DNA corresponding to part of the 5'-untranslated leader. Analysis of clustered point mutants in the HIV-1 leader for DNA-binding and transcription activity in vitro and in vivo suggests a role for LBP-1 as part of the basal promoter. A complex overlapping arrangement is observed between sequences required for the interaction of LBP-1 and CTF/NF I proteins and those defined previously for regulation by the HIV-1 Tat protein.