a–c Different views of the cryo-EM reconstruction of the RNAP-HelD complex. The electron density map is semi-transparent in the same colours as in Fig. 1 with the addition of ε green, and HelD red. The HelD clamp arm (CA), secondary channel arm (SCA), 1 A Torso, and 2 A Head domains are labelled, as are the up- and downstream sides of RNAP (a). The primary channel that is formed between the β and β’ subunits is shown in b, and the secondary channel indicated by the dotted circle in a. The change in orientation between the views in panels a and b is indicated by the arrows, with the right side arrow indicating a rotation of the view in a upwards from the α2/ε end that would move the β’ end down. The left arrow indicates the subsequent 165° clockwise rotation of the complex to give the view in b. The view in c is a simple 90° rotation of the orientation in b.