title: The structure of anE. colitRNAfMetA1-U72variant shows an unusual conformation of the A1-U72base pair.
abstract: Translation initiation in eukaryotes and archaea involves a methionylated initiator tRNA delivered to the ribosome in a ternary complex with e/aIF2 and GTP. Eukaryotic and archaeal initiator tRNAs contain a highly conserved A1-U72base pair at the top of the acceptor stem. The importance of this base pair to discriminate initiator tRNAs from elongator tRNAs has been established previously using genetics and biochemistry. However, no structural data illustrating how the A1-U72base pair participates in the accurate selection of the initiator tRNAs by the translation initiation systems are available. Here, we describe the crystal structure of a mutantE. coliinitiator tRNAfMetA1-U72, aminoacylated with methionine, in which the C1:A72mismatch at the end of the tRNA acceptor stem has been changed to an A1-U72base pair. Sequence alignments show that the mutantE. colitRNA is a good mimic of archaeal initiator tRNAs. The crystal structure, determined at 2.8 Å resolution, shows that the A1-U72pair adopts an unusual arrangement. A1is in asynconformation and forms a single H-bond interaction with U72This interaction requires protonation of the N1 atom of A1Moreover, the 5' phosphoryl group folds back into the major groove of the acceptor stem and interacts with the N7 atom of G2A possible role of this unusual geometry of the A1-U72pair in the recognition of the initiator tRNA by its partners during eukaryotic and archaeal translation initiation is discussed.
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Auriane
authors.initials: A
authors.lastname: Monestier
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Alexey
authors.initials: A
authors.lastname: Aleksandrov
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Pierre-Damien
authors.initials: PD
authors.lastname: Coureux
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Panvert
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Mechulam
authors.affiliation: Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Schmitt
mesh_terms: D000926:Anticodon; D020029:Base Pairing; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D019642:RNA, Archaeal / Q000737:chemistry; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000926:Anticodon; D019642:RNA, Archaeal; D012329:RNA, Bacterial; D012358:RNA, Transfer, Met
keywords: X-ray crystallography; tRNA; translation initiation