Vanyushin B F, Kirnos M D
Biochim Biophys Acta. 1977 Mar 18;475(2):323-36. doi: 10.1016/0005-2787(77)90023-5.
Base composition, content of pyrimidine isopliths and methylation degree of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) from various vertebrates and protozoon Crithidia oncopelti have been studied. mtDNAs from mammals (ox, rat) do not differ in fact in the G + C content from the respective nDNA. The G + C content in mtDNA from fishes (sheat-fish) and birds (duck, chicken) is 1.5--2.5 mol % higher than in the respective nDNA. Kinetoplast DNA (kDNA) from Crithidia oncopelti (G + C = 42.9 mol %) differs significantly in base composition from nDNA (G + C 51.3 mol%). All the mtDNA and kDNA studied differ from the respective nDNA by a lower degree of pyrimidine clustering. The amount of mono- and dipyrimidine fragments in mtDNA is more than 30 mol %, whereas in nDNA it does not exceed 23 mol %. The quantity of long pyrimidine clusters (hexa- and others) is 2--4 times lower in mtDNA than in nDNA. The lower degree of clustering of pyrimidine nucleotides seems to be a specific feature of all the mtDNA studied. This may be indicative of common traits in the organization and origin of mtDNA. All mtDNA of vertebrates contain 5-methylcytosine as "minor" base (1.5--3.15 mol %) and surpass by 1.5--2 times the respective nDNA in the methylation degree. It has been found that in animals mtDNA is species specific as far as the 5-methylcytosine content is concerned. mtDNA of beef heart differs significantly from nDNA in the mode of 5-methylcytosine distribution in pyrimidine isopliths, which may indicate that methylation specificity of nuclear and mitochondrial DNA is not the same. In mitochondria and nuclei of rat liver certain DNA-methylase activity has been detected, which provides in vitro the methylation of cytosine residues both in homologbous DNA and various heterologous DNAs. Specificity of methylation in vitro of cytosine residues in one and the same heterologous DNA from Escherichia coli B with nuclear and mitochondrial enzymes is different. Mitochondrial enzyme methylates cytosine residues chiefly in mono-, whereas nuclear enzyme, in di- and tripyrimidine fragments.
对各种脊椎动物以及原生动物克氏锥虫的线粒体DNA（mtDNA）和核DNA（nDNA）的碱基组成、嘧啶同聚物含量及甲基化程度进行了研究。哺乳动物（牛、大鼠）的mtDNA在G + C含量上与各自的nDNA实际上并无差异。鱼类（鲶鱼）和鸟类（鸭、鸡）的mtDNA中的G + C含量比各自的nDNA高1.5 - 2.5摩尔%。克氏锥虫的动质体DNA（kDNA）（G + C = 42.9摩尔%）在碱基组成上与nDNA（G + C 51.3摩尔%）有显著差异。所研究的所有mtDNA和kDNA与各自的nDNA相比，嘧啶聚类程度较低。mtDNA中单嘧啶和双嘧啶片段的含量超过30摩尔%，而nDNA中不超过23摩尔%。mtDNA中长嘧啶簇（六聚体及其他）的数量比nDNA低2 - 4倍。嘧啶核苷酸较低的聚类程度似乎是所有所研究mtDNA的一个特征。这可能表明mtDNA在组织和起源方面有共同特征。所有脊椎动物的mtDNA都含有5 - 甲基胞嘧啶作为“次要”碱基（1.5 - 3.15摩尔%），甲基化程度比各自的nDNA高1.5 - 2倍。已发现就5 - 甲基胞嘧啶含量而言，动物的mtDNA具有物种特异性。牛心mtDNA在嘧啶同聚物中5 - 甲基胞嘧啶的分布模式上与nDNA有显著差异，这可能表明核DNA和线粒体DNA的甲基化特异性不同。在大鼠肝脏的线粒体和细胞核中检测到了一定的DNA甲基化酶活性，该酶在体外可使同源DNA和各种异源DNA中的胞嘧啶残基甲基化。用核酶和线粒体酶对来自大肠杆菌B的同一种异源DNA中的胞嘧啶残基进行体外甲基化的特异性不同。线粒体酶主要使单嘧啶片段中的胞嘧啶残基甲基化，而核酶使双嘧啶和三嘧啶片段中的胞嘧啶残基甲基化。
