SITE-SPECIFIC CONFORMATIONAL ALTERATION OF THE OCT-1 POU DOMAIN-DNA COMPLEX AS THE BASIS FOR DIFFERENTIAL RECOGNITION BY VMW65 (VP16)

We show that the presence of a regulatory cis-acting element that flan ks the core octamer site and dictates selectivity in the response to V mw65 (VP16), while dispensable for POU binding per se, induces a confo rmational alteration in the nature of the POU domain in the DNA comple x. A single substitution in the flanking signal distorts the POU compl ex and without affecting overall POU binding prevents Vmw65 interactio n. Alternatively, substitution of a residue in the homeodomain predict ed to contact the GARAT region prevents its recognition even on a wild -type motif, causing a reversion to the DNA binding pattern seen on a cellular motif and at the same time inefficient recognition by Vmw65. The results indicate that Vmw65 recognizes a particular POU domain con formation induced by the presence of the flanking GARAT region.