Cryo-EM study of start codon selection during archaeal translation initiation.
Eukaryotic and archaeal translation initiation complexes have a common structural core comprising e/aIF1, e/aIF1A, the ternary complex (TC, e/aIF2-GTP-Met-tRNAiMet) and mRNA bound to the small ribosomal subunit. e/aIF2 plays a crucial role in this process but how this factor controls start codon selection remains unclear. Here, we present cryo-EM structures of the full archaeal 30S initiation complex showing two conformational states of the TC. In the first state, the TC is bound to the ribosome in a relaxed conformation with the tRNA oriented out of the P site. In the second state, the tRNA is accommodated within the peptidyl (P) site and the TC becomes constrained. This constraint is compensated by codon/anticodon base pairing, whereas in the absence of a start codon, aIF2 contributes to swing out the tRNA. This spring force concept highlights a mechanism of codon/anticodon probing by the initiator tRNA directly assisted by aIF2.
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Pierre-Damien
PD
Coureux
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Christine
C
Lazennec-Schurdevin
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Auriane
A
Monestier
Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Eric
E
Larquet
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Lionel
L
Cladière
Department of Structural Biology and Genomics, Institute of Genetics and Molecular and Cellular Biology, Centre National de la Recherche Scientifique (CNRS)/Institut National de la Santé et de la Recherche Médicale (INSERM)/Université Louis Pasteur, BP 10142, 67404 Illkirch, France.
Bruno P
BP
Klaholz
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Emmanuelle
E
Schmitt
Laboratoire de Biochimie, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau cedex, France.
Yves
Y
Mechulam
D000926:Anticodon / Q000378:metabolism; D001105:Archaea / Q000502:physiology*; D019843:Archaeal Proteins / Q000502:physiology* / Q000648:ultrastructure; D020029:Base Pairing / Q000502:physiology; D018387:Codon, Initiator / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D010448:Peptide Initiation Factors / Q000502:physiology* / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000502:physiology; D054749:Ribosome Subunits, Small, Archaeal / Q000502:physiology / Q000648:ultrastructure*
D000926:Anticodon; D019843:Archaeal Proteins; D018387:Codon, Initiator; C118735:IF2 protein, archaeal; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012358:RNA, Transfer, Met