(d) Replication reaction performed as in Fig. 1g. Experiments in (a)-(d) used MCM containing wild type (wt) or S/T-D substitution mutants of Mcm4 and Mcm6 as indicated. In (d), MCM loading was equalised across samples by using 5-fold more mutant than wild type MCM protein, as is shown in Fig. EV6c. 