Selective stimulation of translation of leaderless mRNA by initiation factor 2: evolutionary implications for translation.
Translation initiation in bacteria involves a stochastic binding mechanism in which the 30S ribosomal subunit first binds either to mRNA or to initiator tRNA, fMet-tRNA(f)(Met). Leaderless lambda cI mRNA did not form a binary complex with 30S ribosomes, which argues against the view that ribosomal recruitment signals other than a 5'-terminal start codon are essential for translation initiation of these mRNAs. We show that, in Escherichia coli, translation initiation factor 2 (IF2) selectively stimulates translation of lambda cI mRNA in vivo and in vitro. These experiments suggest that the start codon of leaderless mRNAs is recognized by a 30S-fMet-tRNA(f)(Met)-IF2 complex, an intermediate equivalent to that obligatorily formed during translation initiation in eukaryotes. We further show that leaderless lambda cI mRNA is faithfully translated in vitro in both archaebacterial and eukaryotic translation systems. This suggests that translation of leaderless mRNAs reflects a fundamental capability of the translational apparatus of all three domains of life and lends support to the hypothesis that the translation initiation pathway is universally conserved.
Grill
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Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Dr Bohrgasse 9, 1030 Vienna, Austria.
Gualerzi
C O
CO
Londei
P
P
Bläsi
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D020413:3' Untranslated Regions; D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001667:Binding, Competitive; D005075:Biological Evolution; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; D008957:Models, Genetic; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000378:metabolism*; D039881:Prokaryotic Initiation Factor-2; D012333:RNA, Messenger / Q000378:metabolism*; D012358:RNA, Transfer, Met / Q000378:metabolism; D011817:Rabbits; D012097:Repressor Proteins / Q000235:genetics; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D016944:Sulfolobus / Q000235:genetics; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
D020413:3' Untranslated Regions; D001425:Bacterial Outer Membrane Proteins; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; D010448:Peptide Initiation Factors; D039881:Prokaryotic Initiation Factor-2; D012333:RNA, Messenger; D012358:RNA, Transfer, Met; D012097:Repressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C089238:fMet-tRNA(fMet); C016649:phage repressor proteins; C078167:OMPA outer membrane proteins