A direct real-time spectroscopic investigation of the mechanism of open complex formation by T7 RNA polymerase

The mechanism of unwinding of promoter DNA during the transition from closed to open complexes of T7 RNA polymerase was investigated in real-time by fluorescence spectroscopy. Findings indicated that facile base pair disruption at -1 is sufficient for transcription initiation. It is suggested that the polymerase makes contacts at or near -1 and -6 resulting in untwisting of these base pairs thus producing at least two base pair disruption events at -1 and -6 which are followed by bidirectional propagation to -4.