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首页> 外文期刊>Journal of Molecular Biology >Amino acid acceptor identity switch of Escherichia coli tmRNA from alanine to histidine in vitro.
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Amino acid acceptor identity switch of Escherichia coli tmRNA from alanine to histidine in vitro.

机译：大肠杆菌tmRNA的氨基酸受体同一性在体外从丙氨酸转变为组氨酸。

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According to a trans -translation model, tmRNA facilitates the resumption of translation that has been stalled on the ribosome with the 3' end of a terminator-less mRNA, to produce a chimera polypeptide of the nascent peptide and the tmRNA-encoding 11 amino acid-tag. The first alanine residue of the tag-sequence is encoded neither by mRNA nor by tmRNA. This alanine is a key molecule for this model, in which it is derived from the alanine moiety aminoacylated to tmRNA. This is supported only by the observation that a point mutation at the third base-pair position of the acceptor stem of Escherichia coli tmRNA that deprives it of its aminoacylation ability causes abolishment of tag-peptide synthesis in vitro. Here, we made an E. coli tmRNA mutant with a completely switched amino acid acceptor identity from alanine to histidine by transplanting the upper half of the acceptor stem of tRNAHis. This histidine acceptor tmRNA mutant still retained an ability of tag-specific amino acid incorporation into the polypeptide in an in vitro poly(U)-dependent tag-peptide synthesis system, with an altered amino acid composition. Histidine, which is not a constituent of the original tag-peptide, was incorporated into the mutant-directed tag. The molar ratio of amino acids incorporated is consistent with that in the tag-sequence with the only expected change being the first amino acid from alanine to histidine. These results indicate that the first alanine residue of the tag-peptide is actually derived from that aminoacylated to tmRNA and is substitutable by other amino acids during the trans -translation processes. Copyright 1999 Academic Press.
机译：根据反式翻译模型，tmRNA有助于恢复停在核糖体上的无终止子的mRNA 3'端的翻译，以产生新生肽的嵌合多肽和编码tmRNA的11个氨基酸-标签。标签序列的第一个丙氨酸残基既不由mRNA编码，也不由tmRNA编码。该丙氨酸是该模型的关键分子，其中它衍生自氨酰化为tmRNA的丙氨酸部分。这仅通过以下观察得到支持，即大肠杆菌tmRNA受体茎的第三个碱基对位置的点突变剥夺了其氨酰化能力，从而导致体外标签肽合成的取消。在这里，我们通过移植tRNAHis受体茎的上半部分，制作了一个具有从丙氨酸到组氨酸的氨基酸受体身份完全转换的大肠杆菌tmRNA突变体。该组氨酸受体tmRNA突变体仍保留了在体外聚（U）依赖性标签肽合成系统中标签特异性氨基酸掺入多肽的能力，但氨基酸组成发生了变化。组氨酸不是最初的标签肽的组成部分，被并入突变体定向的标签中。掺入的氨基酸的摩尔比与标签序列中的摩尔比一致，唯一的预期变化是从丙氨酸到组氨酸的第一个氨基酸。这些结果表明，标签肽的第一个丙氨酸残基实际上是由氨基酰化成tmRNA的残基衍生的，并且在反式翻译过程中可以被其他氨基酸取代。版权所有1999，学术出版社。

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