Considering that Mcm10 does not appear to increase the elongation rate of the replisome (Figure 4C), it may not be required at all times. For example, Mcm10 might only be needed to help the replisome bypass blocks on the lagging strand which conceivably could be performed by a dynamic Mcm10 that interacts only transiently with a stalled replisome. Alternatively, Mcm10 mediated isomerization of CMG-DNA may remain stable, in which case Mcm10 may not be needed for some time after its first use, and in fact an Mcm10 effect on CMG that only requires transient Mcm10 binding has been demonstrated in an earlier study (Lõoke et al., 2017).