Helicase asymmetry. The structure of the T7 helicase complexes with the ATP analog AMP-PNP is shown. The three classes of helicase subunits are shown in blue, red, and yellow. The rotation relative to the plane of the hexamer is shown for each subunit. Notice that only four of the subunits, those shown in blue and yellow, bind AMP-PNP.
[Drawn from 1E0K.pdb.]