a, b, The middle domains of FliGFL (a; A. aeolicus, closed) and FLiGMC (b; T. maritima, open). The equivalent position of the extreme clockwise-biased deletion mutant is coloured in magenta. c, d, The C-terminal domains of A. aeolicus FliGFL (CterFL) (c) and T. maritima FliGMC (CterMC) (d). Torque helixC5 is labelled with a red asterisk. Hinge residues M236 and F237 are shown as sticks.