Volkov A, Mascarenhas J, Andrei-Selmer C, Ulrich H D, Graumann P L
Biochemie, Fachbereich Chemie, Philipps-Universität Marburg. Max-Planck Institut für Terrestrische Mikrobiologie, Marburg, Germany.
Mol Cell Biol. 2003 Aug;23(16):5638-50. doi: 10.1128/MCB.23.16.5638-5650.2003.
We show that Bacillus subtilis SMC (structural maintenance of chromosome protein) localizes to discrete foci in a cell cycle-dependent manner. Early in the cell cycle, SMC moves from the middle of the cell toward opposite cell poles in a rapid and dynamic manner and appears to interact with different regions on the chromosomes during the cell cycle. SMC colocalizes with its interacting partners, ScpA and ScpB, and the specific localization of SMC depends on both Scp proteins, showing that all three components of the SMC complex are required for proper localization. Cytological and biochemical experiments showed that dimeric ScpB stabilized the binding of ScpA to the SMC head domains. Purified SMC showed nonspecific binding to double-stranded DNA, independent of Scp proteins or ATP, and was retained on DNA after binding to closed DNA but not to linear DNA. The SMC head domains and hinge region did not show strong DNA binding activity, suggesting that the coiled-coil regions in SMC mediate an association with DNA and that SMC binds to DNA as a ring-like structure. The overproduction of SMC resulted in global chromosome compaction, while SMC was largely retained in bipolar foci, suggesting that the SMC complex forms condensation centers that actively affect global chromosome compaction from a defined position on the nucleoid.
我们发现枯草芽孢杆菌的染色体结构维持蛋白（SMC）以细胞周期依赖性方式定位于离散的焦点区域。在细胞周期早期，SMC以快速且动态的方式从细胞中部移向相对的细胞极，并在细胞周期中似乎与染色体的不同区域相互作用。SMC与其相互作用伴侣ScpA和ScpB共定位，且SMC的特异性定位依赖于这两种Scp蛋白，这表明SMC复合体的所有三个组分对于正确定位都是必需的。细胞学和生化实验表明，二聚体ScpB稳定了ScpA与SMC头部结构域的结合。纯化的SMC显示出与双链DNA的非特异性结合，不依赖于Scp蛋白或ATP，并且在与闭环DNA结合后保留在DNA上，但与线性DNA结合后则不然。SMC头部结构域和铰链区未显示出强的DNA结合活性，这表明SMC中的卷曲螺旋区域介导了与DNA的结合，并且SMC以环状结构与DNA结合。SMC的过量表达导致全局染色体压缩，而SMC主要保留在双极焦点区域，这表明SMC复合体形成了凝聚中心，从类核上的特定位置积极影响全局染色体压缩。
