| The structure of the T. aquaticus holoenzyme shows how the three structural domains of the sigma subunit bind to the core enzyme in a position to recognize the promoter elements. The DNA is numbered relative to the transcription start site at +1. The σ2 domain recognizes the -10 region (red), while the σ3 domain binds to the flanking base pairs of the extended -10 region. The σ4 domain, which binds to the -35 element (red), is anchored to a flexible flap of the β subunit that may allow movement of the σ4 subunit to allow for different spacings between the -35 and -10 regions. (PDB 1IW7) |
