rigid proteinaceous "wedge" (either part of the helicase itself or another associated protein) that separates the DNA strands. Pump model The pump model postulates that multiple helicases load at replication origins, translocate away from one another, and in some manner eventually become anchored in place. They then rotate dsDNA in opposite directions, resulting in the unwinding of the double helix in the intervening region. The pump model has also been proposed to be restricted to the melting of origin DNA while the Mcm2-7 complexes are still anchored at the origin just before replication initiation. Role in cancer Various MCMs have been shown to promote cell proliferation in vitro and in vivo especially in certain types of cancer cell lines. The association between MCMs and proliferation in cancer cell lines is mostly attributed to its ability to enhance DNA replication. The roles of MCM2 and MCM7 in cell proliferation have been demonstrated in various cellular contexts and even in human specimens. MCM2 has been shown to be frequently expressed in proliferating premalignant lung cells. Its expression was associated with cells having a higher proliferation potential in non-dysplastic squamous epithelium, malignant fibrous histiocytomas, and endometrial carcinoma, while MCM2 expression was also correlated higher mitotic index in breast cancer specimens. Similarly, many research studies have shown the link between MCM7 expression and cell proliferation. Expression of MCM7 was significantly correlated with the expression of Ki67 in choriocarcinomas, lung cancer, papillary urothelial neoplasia, esophageal cancer, and endometrial cancer. Its expression was also associated with a higher proliferative index in prostatic intraepithelial neoplasia and cancer. See also Human genes encoding MCM proteins include: MCM2 MCM3 MCM4 MCM5 MCM6 MCM7 MCM8 MCM9 MCM10 References External links macromolecular structures of MCM at the EM Data Bank(EMDB) DNA replication