Muto A, Andachi Y, Yuzawa H, Yamao F, Osawa S
Department of Biology, School of Science, Nagoya University, Japan.
Nucleic Acids Res. 1990 Sep 11;18(17):5037-43. doi: 10.1093/nar/18.17.5037.
The genes for presumably all the tRNA species in Mycoplasma capricolum, a derivative of Gram-positive eubacteria, have been cloned and sequenced. There are 30 genes encoding 29 tRNA species. This number is the smallest in all the known genetic systems except for mitochondria. The sequences of 9 tRNA genes of them have been previously reported (1-3). Twenty-two genes are organized in 5 clusters consisting of nine, five, four and two genes (2 sets), respectively. The other eight genes exist as a single transcription unit. All the tRNAs are encoded each by a single gene, except for the occurrence of two tRNA(Lys)(TTT) genes. The arrangement of tRNA genes in the 9-gene cluster, the 5-gene cluster, the 4-gene cluster and one of the 2-gene clusters reveals extensive similarity with a part of the 21-tRNA gene cluster and/or the 16-tRNA gene cluster in Bacillus subtilis, respectively. The results suggest that the present M. capricolum tRNA genes have evolved from large tRNA gene clusters in the ancestral Gram-positive bacterial genome common to M. capricolum and B. subtilis, by discarding genes for redundant as well as non-obligate tRNAs, so that all the codons may be translated by as small a number of tRNAs as possible.
山羊支原体是革兰氏阳性真细菌的衍生物，其所有可能的tRNA种类的基因已被克隆和测序。有30个基因编码29种tRNA。这个数量是除线粒体之外所有已知遗传系统中最少的。其中9个tRNA基因的序列先前已有报道(1 - 3)。22个基因分别组成5个簇，包含9个、5个、4个和2个基因(2组)。另外8个基因作为单个转录单元存在。除了有两个tRNA(Lys)(TTT)基因外，所有tRNA均由单个基因编码。9基因簇、5基因簇、4基因簇和其中一个双基因簇中的tRNA基因排列，分别与枯草芽孢杆菌中21 - tRNA基因簇和/或16 - tRNA基因簇的一部分显示出广泛的相似性。结果表明，目前山羊支原体的tRNA基因是从山羊支原体和枯草芽孢杆菌共有的祖先革兰氏阳性细菌基因组中的大型tRNA基因簇进化而来，通过丢弃冗余以及非必需tRNA的基因，以便所有密码子都能用尽可能少的tRNA进行翻译。
