title: The role of ribosome recycling factor in dissociation of 70S ribosomes into subunits.
abstract: Protein synthesis is initiated on ribosomal subunits. However, it is not known how 70S ribosomes are dissociated into small and large subunits. Here we show that 70S ribosomes, as well as the model post-termination complexes, are dissociated into stable subunits by cooperative action of three translation factors: ribosome recycling factor (RRF), elongation factor G (EF-G), and initiation factor 3 (IF3). The subunit dissociation is stable enough to be detected by conventional sucrose density gradient centrifugation (SDGC). GTP, but not nonhydrolyzable GTP analog, is essential in this process. We found that RRF and EF-G alone transiently dissociate 70S ribosomes. However, the transient dissociation cannot be detected by SDGC. IF3 stabilizes the dissociation by binding to the transiently formed 30S subunits, preventing re-association back to 70S ribosomes. The three-factor-dependent stable dissociation of ribosomes into subunits completes the ribosome cycle and the resulting subunits are ready for the next round of translation.
authors.affiliation: Department of Microbiology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Go
authors.initials: G
authors.lastname: Hirokawa
authors.forename: Romana M
authors.initials: RM
authors.lastname: Nijman
authors.forename: V Samuel
authors.initials: VS
authors.lastname: Raj
authors.forename: Hideko
authors.initials: H
authors.lastname: Kaji
authors.forename: Kazuei
authors.initials: K
authors.lastname: Igarashi
authors.forename: Akira
authors.initials: A
authors.lastname: Kaji
mesh_terms: D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D020653:Peptide Elongation Factor G / Q000378:metabolism; D039665:Prokaryotic Initiation Factor-3 / Q000378:metabolism; D014176:Protein Biosynthesis; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D020653:Peptide Elongation Factor G; D039665:Prokaryotic Initiation Factor-3; D012269:Ribosomal Proteins; C087267:ribosome releasing factor; D006160:Guanosine Triphosphate