PDF(Pubmed)
Abstract：
In translation initiation in prokaryotes, IF3 recognizes the interaction between the initiator codon of mRNA and the anticodon of fMet-tRNAini and then relocates the fMet-tRNAini 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-tRNAini 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-tRNAini 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.
摘要：
在原核生物的翻译启动中，IF3识别mRNA的起始密码子和fMet-tRNAini的反密码子之间的相互作用，然后将fMet-tRNAini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。在密码子的第一个和第二个碱基，只有沃森-克里克碱基对是可以容忍的。在三垒，更强的碱基对，例如沃森-克里克,更喜欢，但是其他类型的碱基对，例如G/U摆动，也可以耐受；IF3排除了较弱的碱基对。当密码子-反密码子组合对IF3不利或IF3的浓度太低而无法识别任何密码子-反密码子组合时，IF3未能将P位点fMet-tRNAini设置在活性位置并导致其从核糖体脱落。因此，翻译重新起始从A位点处的第二氨酰基-tRNA发生,以产生缺少N-末端fMet的截短的肽。我们将此事件称为N端下降-重新启动。我们还表明，EF-G和RRF参与分解这种带有无活性fMet-tRNAini的异常核糖体复合物，从而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N末端脱落-重新开始。
