Figure 2.

Model for MCM's helicase activity. MCM is shown to 3′-to-5′ translocate along a single strand of DNA that passes through the central cavity of the hexamer, one subunit of which is shown in pale blue. The displaced strand makes transient contacts with the outer surface of the hexamer (Rothenberg et al. 2007; Graham et al. 2011). Residues K323 and R440 of SsoMCM have been implicated in this contact (dark blue spheres) (Graham et al. 2012). (Yellow ribbon) The adjacent PS1BH. Aside from the potential role of these charged residues in contacting the displaced strand, nothing is known regarding the details of the trajectory of the displaced strand on the outer surface of the helicase.