stage as a replicative helicase (19,20). Consistent with this notion, the processivity of the Schizosaccharomyces pombe and mouse Mcm4/6/7 complexes is significantly stimulated on forked DNA structures and it can unwind duplex DNA of 400–500 bp (13,14). Mcm4/6/7 binds to fork and bubble structures in an ATP-dependent manner, and