Brown J R, Doolittle W F
Department of Bioinformatics, SmithKline Beecham Pharmaceuticals, 1250 South Collegeville Road, UP1345, Collegeville PA 19426-0989, USA.
J Mol Evol. 1999 Oct;49(4):485-95. doi: 10.1007/pl00006571.
In translation, separate aminoacyl-tRNA synthetases attach the 20 different amino acids to their cognate tRNAs, with the exception of glutamine. Eukaryotes and some bacteria employ a specific glutaminyl-tRNA synthetase (GlnRS) which other Bacteria, the Archaea (archaebacteria), and organelles apparently lack. Instead, tRNA(Gln) is initially acylated with glutamate by glutamyl-tRNA synthetase (GluRS), then the glutamate moiety is transamidated to glutamine. Lamour et al. [(1994) Proc Natl Acad Sci USA 91:8670-8674] suggested that an early duplication of the GluRS gene in eukaryotes gave rise to the gene for GlnRS-a copy of which was subsequently transferred to proteobacteria. However, questions remain about the occurrence of GlnRS genes among the Eucarya (eukaryotes) outside of the "crown" taxa (animals, fungi, and plants), the distribution of GlnRS genes in the Bacteria, and their evolutionary relationships to genes from the Archaea. Here, we show that GlnRS occurs in the most deeply branching eukaryotes and that putative GluRS genes from the Archaea are more closely related to GlnRS and GluRS genes of the Eucarya than to those of Bacteria. There is still no evidence for the existence of GlnRS in the Archaea. We propose that the last common ancestor to contemporary cells, or cenancestor, used transamidation to synthesize Gln-tRNA(Gln) and that both the Bacteria and the Archaea retained this pathway, while eukaryotes developed a specific GlnRS gene through the duplication of an existing GluRS gene. In the Bacteria, GlnRS genes have been identified in a total of 10 species from three highly diverse taxonomic groups: Thermus/Deinococcus, Proteobacteria gamma/beta subdivision, and Bacteroides/Cytophaga/Flexibacter. Although all bacterial GlnRS form a monophyletic group, the broad phyletic distribution of this tRNA synthetase suggests that multiple gene transfers from eukaryotes to bacteria occurred shortly after the Archaea-eukaryote divergence.
在翻译过程中，不同的氨酰 - tRNA合成酶将20种不同的氨基酸连接到它们各自对应的tRNA上，但谷氨酰胺除外。真核生物和一些细菌使用一种特定的谷氨酰胺 - tRNA合成酶（GlnRS），而其他细菌、古菌（古细菌）和细胞器显然缺乏这种酶。相反，tRNA(Gln)最初由谷氨酰胺 - tRNA合成酶（GluRS）用谷氨酸进行氨酰化，然后谷氨酸部分再转酰胺化为谷氨酰胺。拉穆尔等人[（1994年）《美国国家科学院院刊》91:8670 - 8674]提出，真核生物中GluRS基因的早期复制产生了GlnRS基因——其一个副本随后转移到了变形菌中。然而，关于“冠”类群（动物、真菌和植物）之外的真核生物（真核细胞）中GlnRS基因的存在情况、GlnRS基因在细菌中的分布以及它们与古菌基因的进化关系，仍然存在疑问。在这里，我们表明GlnRS存在于最原始的真核生物中，并且古菌中假定的GluRS基因与真核生物的GlnRS和GluRS基因的关系比与细菌的更密切。仍然没有证据表明古菌中存在GlnRS。我们提出，当代细胞的最后共同祖先，即共同祖先，利用转酰胺作用合成Gln - tRNA(Gln)，并且细菌和古菌都保留了这条途径，而真核生物通过复制现有的GluRS基因发展出了一个特定的GlnRS基因。在细菌中，已经在来自三个高度不同分类群的总共10个物种中鉴定出了GlnRS基因：嗜热栖热菌/耐辐射球菌、γ/β变形菌亚群以及拟杆菌属/噬纤维菌属/屈挠杆菌属。尽管所有细菌的GlnRS形成一个单系群，但这种tRNA合成酶广泛的系统发育分布表明，在古菌 - 真核生物分化后不久，真核生物向细菌发生了多次基因转移。
