Antoun Ayman, Pavlov Michael Y, Lovmar Martin, Ehrenberg Måns
Department of Cell and Molecular Biology, Biomedical Centre, Uppsala University, S-751 24 Uppsala, Sweden.
Mol Cell. 2006 Jul 21;23(2):183-93. doi: 10.1016/j.molcel.2006.05.030.
During initiation of bacterial protein synthesis, messenger RNA and fMet-tRNAfMet bind to the 30S ribosomal subunit together with initiation factors IF1, IF2, and IF3. Docking of the 30S preinitiation complex to the 50S ribosomal subunit results in a peptidyl-transfer competent 70S ribosome. Initiation with an elongator tRNA may lead to frameshift and an aberrant N-terminal sequence in the nascent protein. We show how the occurrence of initiation errors is minimized by (1) recognition of the formyl group by the synergistic action of IF2 and IF1, (2) uniform destabilization of the binding of all tRNAs to the 30S subunit by IF3, and (3) an optimal distance between the Shine-Dalgarno sequence and the initiator codon. We suggest why IF1 is essential for E. coli, discuss the role of the G-C base pairs in the anticodon stem of some tRNAs, and clarify gene expression changes with varying IF3 concentration in the living cell.
在细菌蛋白质合成起始过程中，信使核糖核酸（mRNA）和甲酰甲硫氨酰 - tRNAfMet与起始因子IF1、IF2和IF3一起结合到30S核糖体亚基上。30S起始前复合物与50S核糖体亚基对接，形成具有肽基转移能力的70S核糖体。使用延伸tRNA起始可能导致移码和新生蛋白质中异常的N端序列。我们展示了如何通过以下方式将起始错误的发生率降至最低：（1）IF2和IF1的协同作用识别甲酰基；（2）IF3使所有tRNA与30S亚基的结合均匀不稳定；（3）Shine - Dalgarno序列与起始密码子之间的最佳距离。我们提出了IF1对大肠杆菌至关重要的原因，讨论了某些tRNA反密码子茎中G - C碱基对的作用，并阐明了活细胞中IF3浓度变化时基因表达的变化。
