A new tRNA intermediate revealed on the ribosome during EF4-mediated back-translocation

作者：Connell Sean R; Topf Maya; Qin Yan; Wilson Daniel N; Mielke Thorsten; Fucini Paola; Nierhaus Knud H; Spahn Christian M T^*

来源：Nature Structural & Molecular Biology, 2008, 15(9): 910-915.

DOI：10.1038/nsmb.1469

EF4 (LepA) is an almost universally conserved translational GTPase in eubacteria. It seems to be essential under environmental stress conditions and has previously been shown to back-translocate the tRNAs on the ribosome, thereby reverting the canonical translocation reaction. In the current work, EF4 was directly visualized in the process of back-translocating tRNAs by single-particle cryo-EM. Using flexible fitting methods, we built a model of ribosome-bound EF4 based on the cryo-EM map and a recently published unbound EF4 X-ray structure. The cryo-EM map establishes EF4 as a noncanonical elongation factor that interacts not only with the elongating ribosome, but also with the back-translocated tRNA in the A-site region, which is present in a previously unseen, intermediate state and deviates markedly from the position of a canonical A-tRNA. Our results, therefore, provide insight into the underlying structural principles governing back-translocation.

• 出版日期2008-9
• 单位河北医科大学