Gao Ning, Zavialov Andrey V, Li Wen, Sengupta Jayati, Valle Mikel, Gursky Richard P, Ehrenberg Måns, Frank Joachim
Wadsworth Center, State University of New York at Albany, Empire State Plaza, Albany, New York 12201, USA.
Mol Cell. 2005 Jun 10;18(6):663-74. doi: 10.1016/j.molcel.2005.05.005.
Ribosome recycling, the disassembly of the posttermination complex after each round of protein synthesis, is an essential step in mRNA translation, but its mechanism has remained obscure. In eubacteria, recycling is catalyzed by RRF (ribosome recycling factor) and EF-G (elongation factor G). By using cryo-electron microscopy, we have obtained two density maps, one of the RRF bound posttermination complex and one of the 50S subunit bound with both EF-G and RRF. Comparing the two maps, we found domain I of RRF to be in the same orientation, while domain II in the EF-G-containing 50S subunit is extensively rotated (approximately 60 degrees) compared to its orientation in the 70S complex. Mapping the 50S conformation of RRF onto the 70S posttermination complex suggests that it can disrupt the intersubunit bridges B2a and B3, and thus effect a separation of the two subunits. These observations provide the structural basis for the mechanism by which the posttermination complex is split into subunits by the joint action of RRF and EF-G.
核糖体循环是指每一轮蛋白质合成后终止复合物的解体,它是mRNA翻译过程中的一个关键步骤,但其机制一直不明。在真细菌中,核糖体循环由核糖体循环因子(RRF)和延伸因子G(EF-G)催化。通过冷冻电镜技术,我们获得了两张密度图,一张是RRF结合的终止后复合物的密度图,另一张是同时结合了EF-G和RRF的50S亚基的密度图。比较这两张图,我们发现RRF的结构域I处于相同的方向,而与含EF-G的50S亚基中的结构域II相比,其在70S复合物中的方向发生了大幅旋转(约60度)。将RRF的50S构象映射到70S终止后复合物上表明,它可以破坏亚基间的B2a和B3桥,从而实现两个亚基的分离。这些观察结果为终止后复合物在RRF和EF-G的共同作用下分裂为亚基的机制提供了结构基础。