Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
RNA. 2023 May;29(5):663-674. doi: 10.1261/rna.079447.122. Epub 2023 Feb 8.
In translation initiation in prokaryotes, IF3 recognizes the interaction between the initiator codon of mRNA and the anticodon of fMet-tRNA and then relocates the fMet-tRNA to an active position. Here, we have surveyed 328 codon-anticodon combinations for the preference of IF3. At the first and second base of the codon, only Watson-Crick base pairs are tolerated. At the third base, stronger base pairs, for example, Watson-Crick, are more preferred, but other types of base pairs, for example, G/U wobble, are also tolerated; weaker base pairs are excluded by IF3. When the codon-anticodon combinations are unfavorable for IF3 or the concentration of IF3 is too low to recognize any codon-anticodon combinations, IF3 fails to set the P-site fMet-tRNA at the active position and causes its drop-off from the ribosome. Thereby, translation reinitiation occurs from the second aminoacyl-tRNA at the A site to yield a truncated peptide lacking the amino-terminal fMet. We refer to this event as the amino-terminal drop-off-reinitiation. We also showed that EF-G and RRF are involved in disassembling such an aberrant ribosome complex bearing inactive fMet-tRNA Thereby EF-G and RRF are able to exclude unfavorable codon-anticodon combinations with weaker base pairs and alleviate the amino-terminal drop-off-reinitiation.
在原核生物的翻译起始中，IF3 识别 mRNA 的起始密码子与 fMet-tRNA 的反密码子之间的相互作用，然后将 fMet-tRNA 重新定位到活性位置。在这里，我们调查了 328 个密码子-反密码子组合对 IF3 的偏好。在密码子的第一和第二个碱基上，只允许 Watson-Crick 碱基对。在第三个碱基上，更强的碱基对，例如 Watson-Crick，更受欢迎，但其他类型的碱基对，例如 G/U 摆动，也被容忍；IF3 排除较弱的碱基对。当密码子-反密码子组合不利于 IF3 或 IF3 的浓度太低以至于无法识别任何密码子-反密码子组合时，IF3 无法将 P 位的 fMet-tRNA 设置在活性位置，导致其从核糖体上脱落。因此，翻译从头开始从 A 位的第二个氨酰-tRNA 发生，导致缺少氨基末端 fMet 的截短肽。我们将这种事件称为氨基末端脱落-从头开始。我们还表明，EF-G 和 RRF 参与了这种带有非活性 fMet-tRNA 的异常核糖体复合物的拆卸。因此，EF-G 和 RRF 能够排除具有较弱碱基对的不利密码子-反密码子组合，并减轻氨基末端脱落-从头开始。
