蛋白质翻译是生命活动中的重要环节。众所周知，蛋白质翻译是一个包括起始、延伸、终止和再循环四步的循环过程。每一步都与相应翻译GTP酶及其他翻译因子的帮助。而翻译延伸因子EF-G是唯一一个同时参与延伸与核糖体再循环两个步骤的GTP酶。延伸过程中，EF-G促进(tRNA)2?mRNA由A、P位点移位到P、E位点；在核糖体再循环过程中，EF-G与再循环因子RRF一起将核糖体翻译终止复合物拆分为大小亚基，并释放mRNA与脱酰基的tRNA，以便于下一个翻译循环再利用。因此，对于EF-G的研究有助于加深人类对该过程的理解。
研究人员发现，在EF-G参与核糖体再循环过程中，EF-G能够促进再循环因子RRF结构域的转动，打开核糖体大小亚基间形成的一个主要的亚基桥，从而促进核糖体大小亚基分开以使核糖体进入再循环。实验中研究人员通过一系列蛋白质生化实验和高分辨率的核糖体低温冷冻电镜结构研究，分析到EFG/RRF与翻译终止复合物的相互作用，EFG结构域IV的loop II能够打断30S亚基44螺旋与50S亚基69螺旋之间的亚基桥B2a，才能使核糖体大小亚基分开。
推荐的英文摘要：
Nucleic Acids Research doi: 10.1093/nar/gkv995
New insights into the enzymatic role of EF-G in ribosome recycling
During translation, elongation factor G (EF-G) plays a catalytic role in tRNA translocation and a facilitative role in ribosome recycling. By stabilizing the rotated ribosome and interacting with ribosome recycling factor (RRF), EF-G was hypothesized to induce the domain rotations of RRF, which subsequently performs the function of splitting the major intersubunit bridges and thus separates the ribosome into subunits for recycling. Here, with systematic mutagenesis, FRET analysis and cryo-EM single particle approach, we analyzed the interplay between EF-G/RRF and post termination complex (PoTC). Our data reveal that the two conserved loops (loop I and II) at the tip region of EF-G domain IV possess distinct roles in tRNA translocation and ribosome recycling. Specifically, loop II might be directly involved in disrupting the main intersubunit bridge B2a between helix 44 (h44 from the 30S subunit) and helix 69 (H69 from the 50S subunit) in PoTC. Therefore, our data suggest a new ribosome recycling mechanism which requires an active involvement of EF-G. In addition to supporting RRF, EF-G plays an enzymatic role in destabilizing B2a via its loop II.