Archaeal MCM Proteins as an Analog for the Eukaryotic Mcm2–7 Helicase to Reveal Essential Features of Structure and Function

Figure 1

Mcm2–7 activation and organization. (a) Mcm2–7 rings are loaded as inactive double-hexamers at origins of replication by the Origin Recognition Complex (ORC), Cdc6, and Cdt1 (not shown). In a cell-cycle dependent fashion, the Dbf4-dependent Cdc7 kinase (DDK) and cyclin-dependent kinases (CDKs) drive the association of Cdc45 (red triangle) and the GINS complex (blue oval) with the phosphorylated Mcm2–7 ring to yield the active replicative helicase complex, termed the CMG complex (Cdc45-Mcm2–7-GINS). (b) Schematized view of the Mcm2–7 ring from the N-terminal face with subunits labeled to illustrate the order of subunits around the ring [65, 86]. The ring orientation has been selected to correspond with the orientation of the CMG complex shown in (c). (c) The three-dimensional electron microscopy reconstruction of the CMG complex illustrates basic architectural features. The CMG structure representation was prepared with the UCSF Chimera software package [87] and has been labeled with the Electron Microscopy Data Bank (EMDB) accession number.

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