O'Connor M, Willis N M, Bossi L, Gesteland R F, Atkins J F
Department of Human Genetics, University of Utah, Salt Lake City 84112.
EMBO J. 1993 Jun;12(6):2559-66. doi: 10.1002/j.1460-2075.1993.tb05911.x.
The CCA trinucleotide is a universally conserved feature of the 3' end of tRNAs, where it serves as the site of amino acid attachment. Despite this extreme conservation, we have isolated functional mutants of tRNA(His) and tRNA(Val1) with altered CCA ends. A mutant that leads to de-repression of the histidine biosynthetic operon in Salmonella typhimurium has been characterized and found to have the CCA end of the sole tRNA(His) species mutated to UCA. However, constructed mutants of tRNA(His) with ACA or GCA ends appeared to be nonfunctional in vivo. Mutants of Escherichia coli tRNA(Val1) with GCA or ACA ends were isolated on the basis of their ability to promote frameshifting at a specific sequence. These same tRNA(Val1) mutants also caused read-through of stop codons that were one, or in some instances two, codons downstream of the valine codon decoded by the mutant tRNA. A startling implication of these data is that disruption of interactions between the CCA end of the tRNA and the large ribosomal subunit promotes these aberrant codon-anticodon interactions on the small ribosomal subunit.
CCA三核苷酸是tRNA 3'端普遍保守的特征，它是氨基酸连接的位点。尽管具有这种极端的保守性，但我们已经分离出了CCA末端发生改变的tRNA（His）和tRNA（Val1）功能突变体。已对导致鼠伤寒沙门氏菌中组氨酸生物合成操纵子去阻遏的一个突变体进行了表征，发现其唯一的tRNA（His）物种的CCA末端突变为UCA。然而，构建的具有ACA或GCA末端的tRNA（His）突变体在体内似乎无功能。基于其在特定序列处促进移码的能力，分离出了具有GCA或ACA末端的大肠杆菌tRNA（Val1）突变体。这些相同的tRNA（Val1）突变体还导致了终止密码子的通读，这些终止密码子位于由突变tRNA解码的缬氨酸密码子下游一个密码子处，在某些情况下是两个密码子处。这些数据的一个惊人含义是，tRNA的CCA末端与大核糖体亚基之间相互作用的破坏促进了小核糖体亚基上这些异常的密码子-反密码子相互作用。
