期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11559-11564
DOI：10.1073/pnas.1507703112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIn this work, we dissect the interplay between helix H69 of the large subunit ribosomal RNA, initiation factor IF3, and initiator tRNA, interactions upon which the speed and accuracy of translation initiation rely. Our data clarify the molecular mechanisms that control the initiation process and explain the essentiality of H69 in the cell. Initiation of translation involves the assembly of a ribosome complex with initiator tRNA bound to the peptidyl site and paired to the start codon of the mRNA. In bacteria, this process is kinetically controlled by three initiation factors--IF1, IF2, and IF3. Here, we show that deletion of helix H69 ({triangleup}H69) of 23S rRNA allows rapid 50S docking without concomitant IF3 release and virtually eliminates the dependence of subunit joining on start codon identity. Despite this, overall accuracy of start codon selection, based on rates of formation of elongation-competent 70S ribosomes, is largely uncompromised in the absence of H69. Thus, the fidelity function of IF3 stems primarily from its interplay with initiator tRNA rather than its anti-subunit association activity. While retaining fidelity, {triangleup}H69 ribosomes exhibit much slower rates of overall initiation, due to the delay in IF3 release and impedance of an IF3-independent step, presumably initiator tRNA positioning. These findings clarify the roles of H69 and IF3 in the mechanism of translation initiation and explain the dominant lethal phenotype of the {triangleup}H69 mutation.
