title: Structural insights into initial and intermediate steps of the ribosome-recycling process.
abstract: The ribosome-recycling factor (RRF) and elongation factor-G (EF-G) disassemble the 70S post-termination complex (PoTC) into mRNA, tRNA, and two ribosomal subunits. We have determined cryo-electron microscopic structures of the PoTC·RRF complex, with and without EF-G. We find that domain II of RRF initially interacts with universally conserved residues of the 23S rRNA helices 43 and 95, and protein L11 within the 50S ribosomal subunit. Upon EF-G binding, both RRF and tRNA are driven towards the tRNA-exit (E) site, with a large rotational movement of domain II of RRF towards the 30S ribosomal subunit. During this intermediate step of the recycling process, domain II of RRF and domain IV of EF-G adopt hitherto unknown conformations. Furthermore, binding of EF-G to the PoTC·RRF complex reverts the ribosome from ratcheted to unratcheted state. These results suggest that (i) the ribosomal intersubunit reorganizations upon RRF binding and subsequent EF-G binding could be instrumental in destabilizing the PoTC and (ii) the modes of action of EF-G during tRNA translocation and ribosome-recycling steps are markedly different.
authors.affiliation: Division of Translational Medicine, Wadsworth Center, New York State Department of Health, Albany, NY, USA.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Tanvir R
authors.initials: TR
authors.lastname: Shaikh
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Iwakura
authors.forename: Hideko
authors.initials: H
authors.lastname: Kaji
authors.forename: Akira
authors.initials: A
authors.lastname: Kaji
authors.forename: Rajendra K
authors.initials: RK
authors.lastname: Agrawal
mesh_terms: D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000378:metabolism / Q000648:ultrastructure; D029968:Escherichia coli Proteins / Q000378:metabolism; D020653:Peptide Elongation Factor G / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012335:RNA, Ribosomal / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D020653:Peptide Elongation Factor G; D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; C087267:ribosome releasing factor; C525862:rplK protein, E coli