Butler P J
MRC Laboratory of Molecular Biology, Cambridge, UK.
Philos Trans R Soc Lond B Biol Sci. 1999 Mar 29;354(1383):537-50. doi: 10.1098/rstb.1999.0405.
The tobacco mosaic virus (TMV) particle was the first macromolecular structure to be shown to self-assemble in vitro, allowing detailed studies of the mechanism. Nucleation of TMV self-assembly is by the binding of a specific stem-loop of the single-stranded viral RNA into the central hole of a two-ring sub-assembly of the coat protein, known as the 'disk'. Binding of the loop onto its specific binding site, between the two rings of the disk, leads to melting of the stem so more RNA is available to bind. The interaction of the RNA with the protein subunits in the disk cause this to dislocate into a proto-helix, rearranging the protein subunits in such a way that the axial gap between the rings at inner radii closes, entrapping the RNA. Assembly starts at an internal site on TMV RNA, about 1 kb from its 3'-terminus, and the elongation in the two directions is different. Elongation of the nucleated rods towards the 5'-terminus occurs on a 'travelling loop' of the RNA and, predominantly, still uses the disk sub-assembly of protein subunits, consequently incorporating approximately 100 further nucleotides as each disk is added, while elongation towards the 3'-terminus uses smaller protein aggregates and does not show this 'quantized' incorporation.
烟草花叶病毒（TMV）颗粒是首个被证明能在体外自组装的大分子结构，这使得对其组装机制能够进行详细研究。TMV自组装的成核过程是通过单链病毒RNA的特定茎环结构与外壳蛋白的二环亚组装体（即“盘状体”）的中心孔结合来实现的。该环与盘状体两环之间的特定结合位点结合后，会导致茎部解链，从而使更多的RNA能够结合。RNA与盘状体中蛋白质亚基的相互作用会使盘状体错位形成原螺旋，重新排列蛋白质亚基，使得内环处两环之间的轴向间隙闭合，从而包裹住RNA。组装从TMV RNA上距其3'末端约1 kb的内部位点开始，并且在两个方向上的延伸情况不同。向5'末端延伸的有核杆状结构是在RNA的“移动环”上形成的，并且主要仍然利用蛋白质亚基的盘状亚组装体，因此每添加一个盘状体大约会再结合100个核苷酸，而向3'末端的延伸则使用较小的蛋白质聚集体，并且不会表现出这种“量化”结合。
