Fig. 3. A comparison between the location of the Walker A and B motifs in mtMCM and in two helicase proteins that form hexameric rings, RepA and T7 gp4 (A). The T7 gp4 protein has a primase domain located on the N-terminal end of the protein and a small linker region located between these two domains (Singleton et al., 2000). The mtMCM protein has an N-terminal domain of unknown function, with no homology to any protein other than MCMs. (B) The location of the Walker A (red) and B (green) motifs are shown for the RepA (Niedenzu et al., 2001) and T7 gp4 (Singleton et al., 2000) crystal hexamers.