Replicative helicases unwind DNA exposing the single-stranded template for the replicative polymerases. The MCM helicase motor is loaded onto duplex DNA as an inactive double hexamer in a process that requires an ATPase assembly named ORC and loading factors Cdc6 and Cdt1. Two models exist for how a double hexamer is formed. One model involves the sequential loading of two helicases mediated by one lone ORC complex. According to a second model, two ORC assemblies symmetrically load two MCM helicases to form the double hexamer. We want to use high-resolution single-particle cryo-EM to visualise the entire helicase loading reaction as it occurs in solution.

Relevant papers

Abid Ali F, Douglas ME, Locke J, Pye VE, Nans A, Diffley JF, Costa A CRYO-EM STRUCTURE OF A LICENSED DNA REPLICATION ORIGIN. Nat. Commun. 2017 8 (1), 2241.

Frigola J, He J, Kinkelin K, Pye VE, Renault L, Douglas M, Remus D, Cherepanov P*, Costa A*, Diffley JF* CDT1 STABILISES AN OPEN MCM RING FOR HELICASE LOADING. Nat Commun 2017. In press. (*Corresponding authors).

Costa A.*, Hood I.V.*, Berger J.M. MECHANISMS FOR INITIATING CELLULAR DNA REPLICATION. Annu. Rev. Biochem. 2013;82:25-54. (*Co-first and co-corresponding author).