The structural changes of T7 RNA polymerase from transcription initiation to elongation.

The structures of T7 RNA polymerase (T7 RNAP) captured in the initiation and elongation phases of transcription, as well as an intermediate stage provide insights into how this RNA polymerase protein can initiate RNA synthesis and synthesize 7-10 nucleotides of RNA while remaining bound to the DNA promoter site. Recently, the structures of T7 RNAP bound to its promoter DNA along with either a seven nucleotide or eight nucleotide transcript show an elongated product site resulting from a 40 degrees or 45 degrees rotation of the promoter and domain that binds it. The different functional properties of the initiation and elongation phases of transcription are illuminated from structures of the initiation and elongation complexes. Structural insights into the translocation of the product transcript of RNAP, its separation of the downstream duplex DNA, and its removal of the transcript from the heteroduplex are provided by the structures of several states of nucleotide incorporation. A conformational change in the 'fingers' domain that results from the binding or dissociation of incoming NTP or PPi appears to be associated with the state of translocation of T7 RNAP.