Fig. 1. B2 RNA directly inhibits transcription.

In the absence of B2 RNA, a functional closed preinitiation complex (PIC) can assemble. (Top) This complex can melt the dsDNA duplex, forming an open preinitiation complex to promote transcription initiation. In contrast, B2 RNA directly binds to RNA Pol II in a nonfunctional closed complex. (Bottom) B2 RNA precludes Pol II from making functional DNA contacts and thereby prevents dsDNA melting and open complex formation.