Fig. 7: OCCM maturation to single-loaded hexamer involves duplex DNA translocation by MCM.

a Order of events leading to SH loading onto origin DNA established based on the stepwise disassembly of the ORC/Cdc6 complex, with intermediates stalled by Arginine Finger mutants of MCM. The transition from ATPγS-OCCM to OCCM^Mcm2RA promotes the partial disengagement of Cdc6, Orc2 WHD, Mcm3 WHD and Orc6 from ORC. At the same time, Mcm7 disengages DNA and Mcm2 binds DNA. Transition from OCCM^Mcm2RA to OC₁M^Mcm5RA promotes Cdc6 release, disengagement of the Mcm7 WHD and the stepwise disengagement of the Orc1 ATPase. At the same time Mcm5 binds downstream of the Mcm2 binding site. SH loading upon hydrolysis at the Mcm5-3 ATPase, and possibly other catalytic sites in MCM, promotes Cdt1 release and ORC disengagement from C-terminal MCM. ORC engagement to N-terminal MCM will lead to MO formation and the recruitment of a second MCM hexamer. b Schematic view of protein DNA contacts within ATPγS-OCCM, OCCM^Mcm2RA and OC₁M^Mcm5RA shows that ORC-Cdc6 progressively loosens the DNA grip as MCM translocates away from ORC.