Visualization of release factor 3 on the ribosome during termination of protein synthesis.
Termination of protein synthesis by the ribosome requires two release factor (RF) classes. The class II RF3 is a GTPase that removes class I RFs (RF1 or RF2) from the ribosome after release of the nascent polypeptide. RF3 in the GDP state binds to the ribosomal class I RF complex, followed by an exchange of GDP for GTP and release of the class I RF. As GTP hydrolysis triggers release of RF3 (ref. 4), we trapped RF3 on Escherichia coli ribosomes using a nonhydrolysable GTP analogue. Here we show by cryo-electron microscopy that the complex can adopt two different conformational states. In 'state 1', RF3 is pre-bound to the ribosome, whereas in 'state 2' RF3 contacts the ribosome GTPase centre. The transfer RNA molecule translocates from the peptidyl site in state 1 to the exit site in state 2. This translocation is associated with a large conformational rearrangement of the ribosome. Because state 1 seems able to accommodate simultaneously both RF3 and RF2, whose position is known from previous studies, we can infer the release mechanism of class I RFs.
Department of Biological Sciences, Imperial College London, London SW7 2AY, UK. klaholz@igbmc.u-strasbg.fr
Bruno P
BP
Klaholz
Alexander G
AG
Myasnikov
Marin
M
Van Heel
D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000737:chemistry*; D006160:Guanosine Triphosphate / Q000378:metabolism; D008958:Models, Molecular; D010443:Peptide Chain Termination, Translational; D010454:Peptide Termination Factors / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure
D010454:Peptide Termination Factors; C087971:peptide-chain-release factor 3; D006160:Guanosine Triphosphate; D012343:RNA, Transfer