Boore J L, Brown W M
Department of Biology and Museum of Zoology, University of Michigan, Ann Arbor 48109-1048.
Genetics. 1994 Oct;138(2):423-43. doi: 10.1093/genetics/138.2.423.
The DNA sequence of the 15,532-base pair (bp) mitochondrial DNA (mtDNA) of the chiton Katharina tunicata has been determined. The 37 genes typical of metazoan mtDNA are present: 13 for protein subunits involved in oxidative phosphorylation, 2 for rRNAs and 22 for tRNAs. The gene arrangement resembles those of arthropods much more than that of another mollusc, the bivalve Mytilus edulis. Most genes abut directly or overlap, and abbreviated stop codons are inferred for four genes. Four junctions between adjacent pairs of protein genes lack intervening tRNA genes; however, at each of these junctions there is a sequence immediately adjacent to the start codon of the downstream gene that is capable of forming a stem-and-loop structure. Analysis of the tRNA gene sequences suggests that the D arm is unpaired in tRNA(ser)(AGN), which is typical of metazoan mtDNAs, and also in tRNA(ser)(UCN), a condition found previously only in nematode mtDNAs. There are two additional sequences in Katharina mtDNA that can be folded into structures resembling tRNAs; whether these are functional genes is unknown. All possible codons except the stop codons TAA and TAG are used in the protein-encoding genes, and Katharina mtDNA appears to use the same variation of the mitochondrial genetic code that is used in Drosophila and Mytilus. Translation initiates at the codons ATG, ATA and GTG. A + T richness appears to have affected codon usage patterns and, perhaps, the amino acid composition of the encoded proteins. A 142-bp non-coding region between tRNA(glu) and CO3 contains a 72-bp tract of alternating A and T.
已确定石鳖Katharina tunicata的15532碱基对（bp）线粒体DNA（mtDNA）的DNA序列。后生动物mtDNA典型的37个基因均有存在：13个用于参与氧化磷酸化的蛋白质亚基，2个用于rRNA，22个用于tRNA。基因排列与节肢动物的更为相似，而不像另一种软体动物双壳类紫贻贝。大多数基因直接相邻或重叠，推测有四个基因使用缩写的终止密码子。相邻蛋白质基因对之间的四个连接处缺乏居间的tRNA基因；然而，在这些连接处的每一个，紧挨着下游基因起始密码子都有一个能够形成茎环结构的序列。对tRNA基因序列的分析表明，在tRNA（ser）（AGN）中D臂未配对，这是后生动物mtDNA的典型特征，在tRNA（ser）（UCN）中也是如此，这种情况以前仅在线虫mtDNA中发现。Katharina mtDNA中还有另外两个序列可折叠成类似tRNA的结构；它们是否为功能基因尚不清楚。除了终止密码子TAA和TAG外，所有可能的密码子都用于蛋白质编码基因，Katharina mtDNA似乎使用与果蝇和紫贻贝相同的线粒体遗传密码变体。翻译起始于密码子ATG、ATA和GTG。A+T丰富度似乎影响了密码子使用模式，也许还影响了编码蛋白质的氨基酸组成。tRNA（glu）和CO3之间的一个142bp非编码区包含一段72bp的交替A和T序列。
