Grill S, Gualerzi C O, Londei P, Bläsi U
Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Dr Bohrgasse 9, 1030 Vienna, Austria.
EMBO J. 2000 Aug 1;19(15):4101-10. doi: 10.1093/emboj/19.15.4101.
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.
细菌中的翻译起始涉及一种随机结合机制,其中30S核糖体亚基首先与mRNA或起始tRNA,即甲酰甲硫氨酸-tRNA(f)(Met)结合。无先导序列的λ cI mRNA不会与30S核糖体形成二元复合物,这与以下观点相悖:除了5'末端起始密码子之外的核糖体募集信号对于这些mRNA的翻译起始至关重要。我们表明,在大肠杆菌中,翻译起始因子2(IF2)在体内和体外均选择性地刺激λ cI mRNA的翻译。这些实验表明,无先导序列mRNA的起始密码子由30S-甲酰甲硫氨酸-tRNA(f)(Met)-IF2复合物识别,该复合物相当于真核生物翻译起始过程中必然形成的中间体。我们进一步表明,无先导序列的λ cI mRNA在古细菌和真核生物翻译系统中均可在体外被忠实地翻译。这表明无先导序列mRNA的翻译反映了生命三个域中所有翻译装置的基本能力,并支持了翻译起始途径普遍保守的假说。