Laboratory of Receptor Biology and Gene Expression, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA; Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Laboratory of Receptor Biology and Gene Expression, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
Mol Cell. 2022 Aug 4;82(15):2797-2814.e11. doi: 10.1016/j.molcel.2022.05.016. Epub 2022 Jun 8.
mRNA function is influenced by modifications that modulate canonical nucleobase behavior. We show that a single modification mediates distinct impacts on mRNA translation in a position-dependent manner. Although cytidine acetylation (ac4C) within protein-coding sequences stimulates translation, ac4C within 5' UTRs impacts protein synthesis at the level of initiation. 5' UTR acetylation promotes initiation at upstream sequences, competitively inhibiting annotated start codons. Acetylation further directly impedes initiation at optimal AUG contexts: ac4C within AUG-flanking Kozak sequences reduced initiation in base-resolved transcriptome-wide HeLa results and in vitro utilizing substrates with site-specific ac4C incorporation. Cryo-EM of mammalian 80S initiation complexes revealed that ac4C in the -1 position adjacent to an AUG start codon disrupts an interaction between C and hypermodified t6A at nucleotide 37 of the initiator tRNA. These findings demonstrate the impact of RNA modifications on nucleobase function at a molecular level and introduce mRNA acetylation as a factor regulating translation in a location-specific manner.
mRNA 的功能受修饰的影响，这些修饰调节了典型核碱基的行为。我们表明，单一修饰以位置依赖的方式对 mRNA 翻译产生不同的影响。尽管蛋白编码序列中的胞嘧啶乙酰化（ac4C）刺激翻译，但 5'UTR 中的 ac4C 会在起始水平影响蛋白质合成。5'UTR 乙酰化促进上游序列的起始，竞争性抑制注释的起始密码子。乙酰化进一步直接阻碍最优 AUG 环境的起始：AUG 侧翼 Kozak 序列中的 ac4C 减少了在 HeLa 全转录组范围内以碱基分辨率进行的起始和在体外利用具有特异性 ac4C 掺入的底物的起始。哺乳动物 80S 起始复合物的冷冻电镜显示，AUG 起始密码子旁 -1 位的 ac4C 破坏了起始 tRNA 第 37 位 C 和超修饰 t6A 之间的相互作用。这些发现表明 RNA 修饰在分子水平上对核碱基功能的影响，并将 mRNA 乙酰化作为一种以特定位置调节翻译的因素引入。
