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Nucleic Acids Res. 2008 Sep;36(15):4894-901. doi: 10.1093/nar/gkn462. Epub 2008 Jul 24.

A unique conformation of the anticodon stem-loop is associated with the capacity of tRNAfMet to initiate protein synthesis.

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Laboratoire de Cristallographie et RMN Biologiques, Université Paris Descartes, CNRS, 4 avenue de l'Observatoire, 75006 Paris, France.


In all organisms, translational initiation takes place on the small ribosomal subunit and two classes of methionine tRNA are present. The initiator is used exclusively for initiation of protein synthesis while the elongator is used for inserting methionine internally in the nascent polypeptide chain. The crystal structure of Escherichia coli initiator tRNA(f)(Met) has been solved at 3.1 A resolution. The anticodon region is well-defined and reveals a unique structure, which has not been described in any other tRNA. It encompasses a Cm32*A38 base pair with a peculiar geometry extending the anticodon helix, a base triple between A37 and the G29-C41 pair in the major groove of the anticodon stem and a modified stacking organization of the anticodon loop. This conformation is associated with the three GC basepairs in the anticodon stem, characteristic of initiator tRNAs and suggests a mechanism by which the translation initiation machinery could discriminate the initiator tRNA from all other tRNAs.

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