Figure 4.

A view of the CMG helicase from a cut-away side view in its proposed pumpjack mechanism of Mcm2-7 translocation along ssDNA. The red strand indicates the leading strand DNA. (A) the Mcm2-7 hexamer in its compact state, where the CTD is bound to ssDNA. ssDNA passes through each domain 5′ → 3′ in a clockwise fashion. The black circles in the CTD represent the h2i/ps1β motifs, bound to ssDNA; (B) the Mcm2-7 helicase is in its relaxed configuration with the “horse head” (consisting of subunits 2, 4 and 6) of the pumpjack up. DNA is not entirely bound to the CTD; however, it remains bound to the OB-folds (black circles) of the NTD.