IDENTIFICATION OF A NOVEL CELL-TYPE AND CONTEXT-SPECIFIC ENHANCER WITHIN THE NEGATIVE REGULATORY ELEMENT OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 LONG TERMINAL REPEAT

One segment of the negative regulatory region of the human immunodeficiency virus long terminal repeat (HIV-LTR), nucleotides -273 to -255, is homologous to positive response elements for interleukin-2 and glucocorticoids. We demonstrate that this sequence, referred to as purine-rich response element (PRRE), acts as a classic enhancer in the context of a heterologous promoter, but serves as a functional repressor in the intact provirus, binding (a) cellular factor(s). These data suggest that certain DNA response elements in the HIV LTR serve as negative regulators only in the context of the intact LTR, presumably through interactions with other transcriptional factors, a phenomenon that might be exploited to interfere with viral gene transcription.