title: Allosteric vs. spontaneous exit-site (E-site) tRNA dissociation early in protein synthesis.
abstract: During protein synthesis, deacylated transfer RNAs leave the ribosome via an exit (E) site after mRNA translocation. How the ribosome regulates tRNA dissociation and whether functional linkages between the aminoacyl (A) and E sites modulate the dynamics of protein synthesis have long been debated. Using single molecule fluorescence resonance energy transfer experiments, we find that, during early cycles of protein elongation, tRNAs are often held in the E site until being allosterically released when the next aminoacyl tRNA binds to the A site. This process is regulated by the length and sequence of the nascent peptide and by the conformational state, detected by tRNA proximity, prior to translocation. In later cycles, E-site tRNA dissociates spontaneously. Our results suggest that the distribution of pretranslocation tRNA states and posttranslocation pathways are correlated within each elongation cycle via communication between distant subdomains in the ribosome, but that this correlation between elongation cycle intermediates does not persist into succeeding cycles.
authors.affiliation: Pennsylvania Muscle Institute, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6083, USA.
authors.forename: Chunlai
authors.initials: C
authors.lastname: Chen
authors.forename: Benjamin
authors.initials: B
authors.lastname: Stevens
authors.forename: Jaskiran
authors.initials: J
authors.lastname: Kaur
authors.forename: Zeev
authors.initials: Z
authors.lastname: Smilansky
authors.forename: Barry S
authors.initials: BS
authors.lastname: Cooperman
authors.forename: Yale E
authors.initials: YE
authors.lastname: Goldman
mesh_terms: D000495:Allosteric Site; D000595:Amino Acid Sequence; D001483:Base Sequence; D001693:Biological Transport, Active; D055592:Biophysical Phenomena; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010441:Peptide Chain Elongation, Translational / Q000502:physiology; D014176:Protein Biosynthesis / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D012343:RNA, Transfer