Publication Date:
2008-09-02
Description:
Translation initiation, the rate-limiting step of the universal process of protein synthesis, proceeds through sequential, tightly regulated steps. In bacteria, the correct messenger RNA start site and the reading frame are selected when, with the help of initiation factors IF1, IF2 and IF3, the initiation codon is decoded in the peptidyl site of the 30S ribosomal subunit by the fMet-tRNA(fMet) anticodon. This yields a 30S initiation complex (30SIC) that is an intermediate in the formation of the 70S initiation complex (70SIC) that occurs on joining of the 50S ribosomal subunit to the 30SIC and release of the initiation factors. The localization of IF2 in the 30SIC has proved to be difficult so far using biochemical approaches, but could now be addressed using cryo-electron microscopy and advanced particle separation techniques on the basis of three-dimensional statistical analysis. Here we report the direct visualization of a 30SIC containing mRNA, fMet-tRNA(fMet) and initiation factors IF1 and GTP-bound IF2. We demonstrate that the fMet-tRNA(fMet) is held in a characteristic and precise position and conformation by two interactions that contribute to the formation of a stable complex: one involves the transfer RNA decoding stem which is buried in the 30S peptidyl site, and the other occurs between the carboxy-terminal domain of IF2 and the tRNA acceptor end. The structure provides insights into the mechanism of 70SIC assembly and rationalizes the rapid activation of GTP hydrolysis triggered on 30SIC-50S joining by showing that the GTP-binding domain of IF2 would directly face the GTPase-activated centre of the 50S subunit.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Simonetti, Angelita -- Marzi, Stefano -- Myasnikov, Alexander G -- Fabbretti, Attilio -- Yusupov, Marat -- Gualerzi, Claudio O -- Klaholz, Bruno P -- England -- Nature. 2008 Sep 18;455(7211):416-20. doi: 10.1038/nature07192. Epub 2008 Aug 31.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Genetics and of Molecular and Cellular Biology, Department of Structural Biology and Genomics, Illkirch F-67404, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18758445" target="_blank"〉PubMed〈/a〉
Keywords:
Cryoelectron Microscopy
;
Crystallography, X-Ray
;
Guanosine Triphosphate/chemistry/metabolism
;
Models, Molecular
;
Multiprotein Complexes/*chemistry/genetics/metabolism/*ultrastructure
;
*Peptide Chain Initiation, Translational
;
Prokaryotic Initiation Factor-1/chemistry/genetics/metabolism/ultrastructure
;
Prokaryotic Initiation Factor-2/chemistry/genetics/metabolism/ultrastructure
;
Protein Conformation
;
RNA, Messenger/chemistry/genetics/metabolism
;
RNA, Transfer, Met/chemistry/genetics/metabolism/ultrastructure
;
Ribosome Subunits/chemistry/metabolism/ultrastructure
;
Ribosomes/chemistry/*metabolism/*ultrastructure
;
Thermus thermophilus/*enzymology/genetics/*ultrastructure
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
Permalink
