title: A translocation-associated ribosomal conformational change detected by hydrogen exchange and sedimentation velocity.
abstract: Translocation in ribosomes consists of transposition of peptidyl-tRNA from the aminoacyl to the peptidyl site and, probably concomitantly, the movement of ribosomes on mRNA. Does a conformational change in the ribosome provide the motive force for this process? Hydrogen exchange and sedimentation velocity experiments indicate that the Escherichia coli ribosome does undergo a conformational change associated with translocation. When pretranslocational ribosomes carrying acetyldiphenylalanyl-tRNA in the aminoacyl site were incubated with G factor and GTP, translocation occurred, with a concomitant increase in hydrogen exchange rate and a decrease in sedimentation constant. These changes did not occur when GTP was replaced by a nonhydrolyzable analogue, GDP-CH(2)-P, and they were blocked by the antibiotics fusidic acid and thiostrepton. When posttranslocational ribosomes were cycled back to the pretranslocational state by T factor, GTP, and phenylalanyl-tRNA, the sedimentation constant reverted to the original value. Whether or not this conformation change drives translocation requires further study.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001665:Binding Sites; D002247:Carbon Isotopes; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D055598:Chemical Phenomena; D002621:Chemistry; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005672:Fusidic Acid / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000378:metabolism; D006859:Hydrogen / Q000032:analysis; D010455:Peptides / Q000494:pharmacology; D010649:Phenylalanine / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium
chemical_list: D000900:Anti-Bacterial Agents; D002247:Carbon Isotopes; D006150:Guanine Nucleotides; D010455:Peptides; D012333:RNA, Messenger; D014316:Tritium; D010649:Phenylalanine; D005672:Fusidic Acid; D006859:Hydrogen; D012343:RNA, Transfer