title: The Cryo-EM structure of a complete 30S translation initiation complex from Escherichia coli.
abstract: Formation of the 30S initiation complex (30S IC) is an important checkpoint in regulation of gene expression. The selection of mRNA, correct start codon, and the initiator fMet-tRNA(fMet) requires the presence of three initiation factors (IF1, IF2, IF3) of which IF3 and IF1 control the fidelity of the process, while IF2 recruits fMet-tRNA(fMet). Here we present a cryo-EM reconstruction of the complete 30S IC, containing mRNA, fMet-tRNA(fMet), IF1, IF2, and IF3. In the 30S IC, IF2 contacts IF1, the 30S subunit shoulder, and the CCA end of fMet-tRNA(fMet), which occupies a novel P/I position (P/I1). The N-terminal domain of IF3 contacts the tRNA, whereas the C-terminal domain is bound to the platform of the 30S subunit. Binding of initiation factors and fMet-tRNA(fMet) induces a rotation of the head relative to the body of the 30S subunit, which is likely to prevail through 50S subunit joining until GTP hydrolysis and dissociation of IF2 take place. The structure provides insights into the mechanism of mRNA selection during translation initiation.
authors.affiliation: Structural Biology Unit, Center for Cooperative Research in Biosciences (CIC bioGUNE), Parque Tecnológico de Bizkaia, Derio, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Julián
authors.forename: Pohl
authors.initials: P
authors.lastname: Milon
authors.forename: Xabier
authors.initials: X
authors.lastname: Agirrezabala
authors.forename: Gorka
authors.initials: G
authors.lastname: Lasso
authors.forename: David
authors.initials: D
authors.lastname: Gil
authors.forename: Marina V
authors.initials: MV
authors.lastname: Rodnina
authors.forename: Mikel
authors.initials: M
authors.lastname: Valle
mesh_terms: D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000235:genetics; D008958:Models, Molecular; D008968:Molecular Conformation; D010448:Peptide Initiation Factors / Q000737:chemistry* / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000378:metabolism; D054680:Ribosome Subunits, Small, Bacterial / Q000648:ultrastructure*
chemical_list: D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012358:RNA, Transfer, Met; C089238:fMet-tRNA(fMet)