The Rous sarcoma virus long terminal repeat promoter is regulated by TFII-I

Many viral genes contain core promoters with two basal control elements, th e TATA box and the pyrimidine-rich initiator (Inr). However, the molecular mechanisms involved in transcription initiation from composite core promote rs (TATA(+) Inr(+)) containing Inr elements are unclear. The Rous sarcoma v irus (RSV) long terminal repeat (LTR) contains a transcriptionally potent e nhancer and core promoter composed of a TATA box and an Inr-like sequence, termed the transcription start site core (TSSC). Previously we demonstrated that the TSSC binds the multifunctional Inr-binding protein YY1. Here we p resent evidence that the TSSC also binds the multifunctional transcription factor TFII-I and that both TFII-I and WI are required for RSV LTR transcri ptional activity. Gel shift assays using anti-TFII-I antibody show that TFI I-I is present in a protein complex that specifically binds to the TSSC. Mu tations in the TSSC that reduce TFII-I binding also reduce RSV LTR enhancer and promoter activity. Transient-transfection assays demonstrate that TFII -I transactivates the RSV LTR from ca. fourfold (basal) to ca. sevenfold (e nhanced) in both human and natural host cell lines. Importantly, the activi ty of the TSSC element can be attributed to the binding activity of TFII-I and the WI protein, since mutation of each of these binding sites within th e TSSC element abolishes all viral expression as demonstrated by transient transfection assays. Taken together, these data demonstrate that expression of RSV viral mRNA is dependent on both TFII-I and YY1.