We also examined the effect of Mcm10 on CMG encounter with dual biotin-streptavidin blocks on the leading strand. We showed earlier (Figure 5—figure supplement 1) that CMG is unable to unwind the DNA in the presence of streptavidin and that while CMG-Mcm10 is also strongly inhibited, it unwinds a detectable amount of the DNA within 10 min. To test whether the observed unwinding by CMG-Mcm10 through leading strand blocks is due to streptavidin bypass or streptavidin displacement we repeated the experiment with the 32P-label on the biotinylated strand and using the excess biotin trap. The results demonstrate that streptavidin is displaced from the unwound product (Figure 6B). Hence, Mcm10 appears to provide CMG with more translocation force than CMG alone, consistent with the increase in processivity of CMG in the presence of Mcm10 (Figure 3).