Frameshift suppression at tandem AGA and AGG codons by cloned tRNA genes: assigning a codon to argU tRNA and T4 tRNA(Arg).
Frameshift suppression at tandem AGA and AGG codons by cloned tRNA genes: assigning a codon to argU tRNA and T4 tRNA(Arg).
复制标题
通过克隆的 tRNA 基因对串联 AGA 和 AGG 密码子进行移码抑制：将密码子分配给 argU tRNA 和 T4 tRNA(Arg)。
作者：
R. Spanjaard;Ken;Ken;James R Walker;J. Duin
精氨酸由CGN(N=G、A、U、C)、AGA和AGG编码。在大肠杆菌中，几乎没有AGA和AGG的tRNA，几乎所有的基因都强烈避免使用这些密码子。最近，我们证明了在mRNA中串联的AGA或AGG密码子的存在会导致高频率的移码。在这里，我们证明了当tRNA(T4Arg)或大肠杆菌tRNA(argu，Arg)的基因转化细胞时，相移可以被抑制，证明这种错误是tRNA耗尽的结果。噬菌体T4编码的tRNA(Arg)(反密码子UCU)纠正了AGA-AGA处的移位，但不能纠正AGG-AGG处的移位，表明该tRNA只能阅读AGA。同样，比较argu(Ts)突变体及其同基因野生型亲本的翻译效率表明，argu tRNA(反密码子UCU)读取AGA而不是AGG。在42摄氏度下，argu(Ts)突变体几乎不能阅读AGA-AGA，但agg-agg的翻译几乎不会受到影响。Argu+的过度表达解除了密码子的特异性。Argu中的温度敏感突变体，以前被称为dna Y，因为它在DNA复制方面存在缺陷，可以通过tRNA(T4Arg)基因补充生长。这意味着，Argu基因产物的唯一功能是维持蛋白质合成，它在复制过程中的作用可能是间接的。
Arginine is coded for by CGN (N = G, A, U, C), AGA and AGG. In Escherichia coli there is little tRNA for AGA and AGG and the use of these codons is strongly avoided in virtually all genes. Recently, we demonstrated that the presence of tandem AGA or AGG codons in mRNA causes frameshifts with high frequency. Here, we show that phaseshifts can be suppressed when cells are transformed with the gene for tRNA(T4Arg) or E. coli tRNA(argU,Arg) demonstrating that such errors are the result of tRNA depletion. Bacteriophage T4 encoded tRNA(Arg) (anticodon UCU) corrects shifts at AGA-AGA but not at AGG-AGG, suggesting that this tRNA can only read AGA. Similarly, comparison of the translational efficiencies in an argU (Ts) mutant and in its isogenic wild type parent indicates that argU tRNA (anticodon UCU) reads AGA but not AGG. An argU (Ts) mutant barely reads through AGA-AGA at 42 degrees C but translation of AGG-AGG is hardly, if at all, affected. Overexpression of argU+ relaxes the codon specificity. The thermosensitive mutant in argU, previously called dnaY because it is defective in DNA replication, can be complemented for growth by the gene for tRNA(T4Arg). This implies that the sole function of the argU gene product is to sustain protein synthesis and that its role in replication is probably indirect.