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Systematic Evolution and Study of UAGN Decoding tRNAs in a Genomically Recoded Bacteria

机译:基因组编码细菌中UAGN编码tRNA的系统进化和研究

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摘要

We report the first systematic evolution and study of tRNA variants that are able to read a set of UAGN (N = A, G, U, C) codons in a genomically recoded E. coli strain that lacks any endogenous in-frame UAGN sequences and release factor 1. Through randomizing bases in anticodon stem-loop followed by a functional selection, we identified tRNA mutants with significantly improved UAGN decoding efficiency, which will augment the current efforts on genetic code expansion through quadruplet decoding. We found that an extended anticodon loop with an extra nucleotide was required for a detectable efficiency in UAGN decoding. We also observed that this crucial extra nucleotide was converged to a U (position 33.5) in all of the top tRNA hits no matter which UAGN codon they suppress. The insertion of U33.5 in the anticodon loop likely causes tRNA distortion and affects anticodon-codon interaction, which induces +1 frameshift in the P site of ribosome. A new model was proposed to explain the observed features of UAGN decoding. Overall, our findings elevate our understanding of the +1 frameshift mechanism and provide a useful guidance for further efforts on the genetic code expansion using a non-canonical quadruplet reading frame.
机译:我们报道了tRNA变体的第一个系统进化和研究,该变体能够读取基因组编码的大肠杆菌菌株中缺乏任何内源框内UAGN序列的UAGN(N = A,G,U,C)密码子。释放因子1.通过随机选择反密码子茎环中的碱基,然后进行功能选择,我们鉴定出具有显着提高的UAGN解码效率的tRNA突变体,这将增加当前通过四联体解码进行遗传密码扩展的工作。我们发现,为了在UAGN解码中达到可检测的效率,需要使用带有额外核苷酸的扩展反密码子环。我们还观察到,无论它们抑制哪种UAGN密码子,在所有顶部tRNA命中中,这个至关重要的额外核苷酸都已收敛至U(位置33.5)。 U33.5在反密码子环中的插入可能会引起tRNA畸变并影响反密码子与密码子的相互作用,从而在核糖体的P位点诱导+1移码。提出了一种新模型来解释UAGN解码的观察特征。总体而言,我们的发现提高了我们对+1移码机制的理解,并为使用非规范四联阅读框进行遗传密码扩展的进一步努力提供了有用的指导。

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