MCM（Mini-chromosome maintenance）蛋白被普遍认为是所有真核生物DNA复制所必需的DNA解旋酶，不仅仅在DNA复制起始的控制、复制叉的组装及其行进过程起着重要作用，还参与基因组复制与细胞周期之间的偶联调控。最近一些研究发现MCM蛋白除了经典的六聚体环状结构外，还可能形成双六聚体等构象。MCM为什么形成双六聚体构象？这种构象与MCM活性有什么关系？前期已经获得的MCM分子进化树等结果已暗示极端嗜热冰岛硫化叶菌与酵母中存在保守的双六聚体形成机制。本项目将同时采用这两种各具优势的模式材料，首先对由单亚基组成的冰岛硫化叶菌SisMCM同聚体运用遗传、生化与电镜等手段解析双六聚体构象形成机制、动态变化及其生理功能；然后在酵母MCM2-7六个亚基中相应的保守功能域进行突变或互补分析，探讨MCM蛋白构象与其解旋酶活性之间的关系，将有助于解决"MCM悖论"等悬而未决的问题。

MCM（Mini-chromosome maintenance）protein is essential for genome replication in all eukaryotes, which plays important roles both as the licensing factor during initiation and as the coordinator between replication fork movement and the cell cycle progression. Recent studies showed that MCM might form double hexamers (DH) in vivo and in vitro besides its traditional single hexamer ring shape. What's the physiological function of such particular conformation of MCM remains elusive. The mechanism to form doule-hexamer structure may be conserved among archaeal and eukaryotic MCM proteins through our previous phylogenetic tree analysis. Hyperthermophilic Sulfolobus islandicus becomes an ideal model organism because this genetically tractable species contains only one MCM protein, which makes it possible to carry out the structural and functional analysis for homo-oligomer of MCM. We'll investigate the ability and mechanism of SisMCM to form double hexamers through combination of approaches as Electro-microscopy and mutation assays. The effects of the DH formation on its unwinding activity will be measured. The results from SisMCM will be further applied to MCM2-7 of Saccharomyces cerevisiae, in which multiple mutations can be easily achieved. By taking advantage of both Sulfolobus and budding yeast models，it might be possible to answer how and why MCM complex should be assembled as the DH form. Our studies may contribute to dissolve the enigmas as "MCM paradox".