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Cohesin is a protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis. == Structure == In all cases where cohesin complexes have been isolated so far, four core subunits have been identified (Fig. 1A; Table 1). The topology and structure of these subunits has been best characterized in budding yeast (Haering et al. 2002, 2004), but the sequence conservation of these proteins and biochemical and electron microscopic observations imply that cohesin complexes in other species are very similar in their structure, (). Cohesin is made up of four subunits, (Scc1 ), (Scc3 ), (Smc1 ) and (Smc3 ). Smc1 and Smc3 are members of the Structural Maintenance of Chromosomes (SMC) family. SMC proteins have two main structural characteristics: an ATP-binding cassette-like 'head' domain with ATPase activity (formed by the interaction of the N- and C- terminals) and a hinge domain that allows dimerization of SMCs. The head and the hinge domains are connected to each other via long anti-parallel coiled coils. The dimer is present in a V-shaped form, connected by the hinges. Upon ATP binding, the two head domains in the dimer bind to each other, forming a ring structure. ATP hydrolysis can therefore trigger opening and closing of the ring. Scc1 and Scc3 bind the ATPase domains of Smc1 and Smc3 stabilizing the ring structure. Scc1 is a member of the kleisin protein family and it controls sister-chromatid separation. The amino and carboxy terminus of Scc1 bind Smc1 and Smc3. Once Scc1 binds on the SMC proteins, Scc3 can also associate by binding with the C-terminal region of Scc1. When Scc1 binds on both Smc1 and Smc3, the cohesin complex forms a closed ring structure. When it binds to only one of the SMC proteins, the complex forms an open ring. However more recently cohesin rings were found to dimerise, with two rings held together by the Scc3 subunit in a handcuff shape, one strand of DNA in each cohesin ring. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cohesin」の詳細全文を読む スポンサード リンク
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