S we failed to detect any Sp1 at the PP5*/ 5'LTR junction or in the coding region of the HIV genome (Figure 5B, bars 1, 2, 5 and 6). Thus, the absence of Sp1 at the 5'LTR in untreated cells is a result of TI due to the actively transcribed PP5* gene. The finding that TNF- stimulation increased the levels of Sp1 not only at the 3' but also at the 5'LTR indicates that stimulating PIC assembly on the