COCRYSTAL STRUCTURE OF YY1 BOUND TO THE ADENOASSOCIATED VIRUS P5 INITIATOR

Ying-Yang 1 protein (YY1) supports specific, unidirectional initiation of messenger RNA production by RNA polymerase II from two adjacent st art sites in the adeno-associated virus P5 promoter, a process which i s independent of the TATA box-binding protein (TBP), The 2.5-Angstrom resolution YY1-initiator element cocrystal structure reveals four zinc fingers recognizing a YY1-binding consensus sequence, Upstream of the transcription start sites protein-DNA contacts involve both strands a nd downstream they are virtually restricted to the template strand, pe rmitting access to the active center of RNA polymerase II and ensuring specificity and directionality. The observed pattern of protein-DNA c ontacts also explains YY1 binding to a preformed transcription bubble, and YY! binding to a DNA/RNA hybrid analog of the P5 promoter region containing a nascent RNA transcript, A model is proposed for YY1-direc ted, TBP-independent transcription initiation.