Boer P H, Gray M W
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada.
Curr Genet. 1988 Dec;14(6):583-90. doi: 10.1007/BF00434084.
Only three tRNA genes are present within a sequenced 12.35 kbp region of the 15.8 kbp mtDNA of Chlamydomonas reinhardtii, a unicellular green alga. The corresponding tRNAs, whose anticodons are specific for TGG (Trp), CAA/G (Gln) and ATG (Met) codons, all display conventional secondary structures. The tRNA(Met) gene encodes an elongator rather than initiator species. The standard genetic code is used in C. reinhardtii mitochondria, but codon distribution is highly biased: in a collection of six identified protein coding genes, nine codons (including TGA) are not used at all, while four other sense codons occur very infrequently. In spite of the absence of certain codons, a minimum of 23 tRNAs (assuming separate initiator and elongator tRNAs(Met) are used) is needed to translate the C. reinhardtii mitochondrial genetic code. It appears unlikely that this minimal tRNA set is encoded by C. reinhardtii mtDNA.
在单细胞绿藻莱茵衣藻15.8kbp的线粒体DNA（mtDNA）中，经测序的12.35kbp区域内仅存在3个tRNA基因。相应的tRNA，其反密码子分别特异性对应TGG（色氨酸）、CAA/G（谷氨酰胺）和ATG（甲硫氨酸）密码子，均呈现传统的二级结构。tRNA（甲硫氨酸）基因编码的是延长因子而非起始因子类型。莱茵衣藻线粒体使用标准遗传密码，但密码子分布存在高度偏倚：在6个已鉴定的蛋白质编码基因集合中，9个密码子（包括TGA）根本未被使用，而其他4个有义密码子出现频率极低。尽管某些密码子不存在，但要翻译莱茵衣藻线粒体遗传密码，至少需要23个tRNA（假设使用单独的起始因子和延长因子tRNA（甲硫氨酸））。看来这个最小的tRNA集合不太可能由莱茵衣藻mtDNA编码。
