Translation initiation by cap‐dependent ribosome recruitment: Recent insights and open questions

• Published in: Wiley interdisciplinary reviews. RNA 2018-07, Vol.9 (4), p.e1473-n/a
• Main Authors: Shirokikh, Nikolay E., Preiss, Thomas
• Format: Article
• Language: English
• Subjects: 5' Untranslated Regions; Elongation; eukaryotic translation initiation; Footprinting; Gene expression; Initiation factors; Intermediates; mRNA translation; Next-generation sequencing; post‐transcriptional gene regulation; Protein biosynthesis; protein synthesis; ribosome; Ribosomes; scanning; start codon recognition; Translation elongation; Translation termination
• ISSN: 1757-7004; 1757-7012
• DOI: 10.1002/wrna.1473

Gene expression universally relies on protein synthesis, where ribosomes recognize and decode the messenger RNA template by cycling through translation initiation, elongation, and termination phases. All aspects of translation have been studied for decades using the tools of biochemistry and molecular biology available at the time. Here, we focus on the mechanism of translation initiation in eukaryotes, which is remarkably more complex than prokaryotic initiation and is the target of multiple types of regulatory intervention. The “consensus” model, featuring cap‐dependent ribosome entry and scanning of mRNA leader sequences, represents the predominantly utilized initiation pathway across eukaryotes, although several variations of the model and alternative initiation mechanisms are also known. Recent advances in structural biology techniques have enabled remarkable molecular‐level insights into the functional states of eukaryotic ribosomes, including a range of ribosomal complexes with different combinations of translation initiation factors that are thought to represent bona fide intermediates of the initiation process. Similarly, high‐throughput sequencing‐based ribosome profiling or “footprinting” approaches have allowed much progress in understanding the elongation phase of translation, and variants of them are beginning to reveal the remaining mysteries of initiation, as well as aspects of translation termination and ribosomal recycling. A current view on the eukaryotic initiation mechanism is presented here with an emphasis on how recent structural and footprinting results underpin axioms of the consensus model. Along the way, we further outline some contested mechanistic issues and major open questions still to be addressed. This article is categorized under: Translation > Translation Mechanisms Translation > Translation Regulation RNA Interactions with Proteins and Other Molecules > Protein–RNA Interactions: Functional Implications Eukaryotic translation initiation involves small ribosomal subunit cap attachment, mRNA scanning, and start codon recognition, followed by large ribosomal subunit joining, and involves a remarkably extended set of initiation factors providing complex control of gene expression.