Loughran Gary, Firth Andrew E, Atkins John F, Ivanov Ivaylo P
School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland.
Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom.
PLoS One. 2018 Feb 22;13(2):e0192648. doi: 10.1371/journal.pone.0192648. eCollection 2018.
The efficiency of start codon selection during ribosomal scanning in eukaryotic translation initiation is influenced by the context or flanking nucleotides surrounding the AUG codon. The levels of eukaryotic translation initiation factors 1 (eIF1) and 5 (eIF5) play critical roles in controlling the stringency of translation start site selection. The basic leucine zipper and W2 domain-containing proteins 1 and 2 (BZW1 and BZW2), also known as eIF5-mimic proteins, are paralogous human proteins containing C-terminal HEAT domains that resemble the HEAT domain of eIF5. We show that translation of mRNAs encoding BZW1 and BZW2 homologs in fungi, plants and metazoans is initiated by AUG codons in conserved unfavorable initiation contexts. This conservation is reminiscent of the conserved unfavorable initiation context that enables autoregulation of EIF1. We show that overexpression of BZW1 and BZW2 proteins enhances the stringency of start site selection, and that their poor initiation codons confer autoregulation on BZW1 and BZW2 mRNA translation. We also show that overexpression of these two proteins significantly diminishes the effect of overexpressing eIF5 on stringency of start codon selection, suggesting they antagonize this function of eIF5. These results reveal a surprising role for BZW1 and BZW2 in maintaining homeostatic stringency of start codon selection, and taking into account recent biochemical, genetic and structural insights into eukaryotic initiation, suggest a model for BZW1 and BZW2 function.
在真核生物翻译起始过程中，核糖体扫描期间起始密码子选择的效率受AUG密码子周围的上下文或侧翼核苷酸的影响。真核生物翻译起始因子1（eIF1）和5（eIF5）的水平在控制翻译起始位点选择的严格性方面发挥着关键作用。含碱性亮氨酸拉链和W2结构域的蛋白1和2（BZW1和BZW2），也被称为eIF5模拟蛋白，是人类旁系同源蛋白，其C端含有类似eIF5的HEAT结构域。我们发现，真菌、植物和后生动物中编码BZW1和BZW2同源物的mRNA的翻译由保守的不利起始上下文中的AUG密码子起始。这种保守性让人联想到能够实现EIF1自我调节的保守不利起始上下文。我们发现，BZW1和BZW2蛋白的过表达增强了起始位点选择的严格性，且它们不佳的起始密码子赋予了BZW1和BZW2 mRNA翻译自我调节能力。我们还发现，这两种蛋白的过表达显著削弱了过表达eIF5对起始密码子选择严格性的影响，表明它们拮抗eIF5的这一功能。这些结果揭示了BZW1和BZW2在维持起始密码子选择的稳态严格性方面的惊人作用，并结合最近对真核生物起始的生化、遗传和结构方面的见解，提出了一个BZW1和BZW2功能的模型。
