FIG. 10.

Model for the mechanism of Sp1(I) site-dependent silencing of the hLHR gene transcription by EAR3. EAR3 bound to the DR motif interacts with Sp1/Sp3 bound to the Sp1(I) site. Such interaction significantly prevents the robust association of TFIIB to the Sp1(I) site without affecting the recruitment of TFIIB to the hLHR gene core promoter region. Anchoring of the TFIIB at the Sp1(I) site does not require prior binding of EAR3 to its cognate site, since the association is clearly present in the absence of EAR3. We propose that interaction of TFIIB with Sp1/Sp3 is indirectly bridged by a currently unidentified protein(s), as indicated by an open circle (putative tethering protein [PTP]). The EAR3-reduced association of TFIIB to the Sp1/Sp3-DNA complex may induce a nonproductive or less-productive form of PIC, in which the recruitment of RNA Pol II to the hLHR promoter was decreased when the hLHR gene was subjected to a repressed state by EAR3 in JAR cells. Inr, initiator element; TSS, transcriptional start site.