The structure of animal mitochondrial DNA (base composition, pyrimidine clusters, character of methylation)

Summary Base composition, content of pyrimidine isopliths and the degree of methylation of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) from various vertebrates and protozoonCrithidia oncopelti have been studied. MtDNAs from mammals (ox, rat) do not differ in fact in the GC content from the resp...
Ausführliche Beschreibung

Summary Base composition, content of pyrimidine isopliths and the degree of methylation of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) from various vertebrates and protozoonCrithidia oncopelti have been studied. MtDNAs from mammals (ox, rat) do not differ in fact in the GC content from the respective nDNA. The GC content in mtDNA from fishes (sheat fish) and birds (duck, chicken) is 1.5–2.5 mole % higher than in the respective nDNA. Kinetoplast DNA (kDNA) fromCrithidia oncopelti (GC = 42.9 mole %) differs significantly in base composition from nDNA (GC = 51.3 mole %). All the mtDNA and kDNA studied differ from the respective nDNA by a lower degree of pyrimidine clustering. Thę amount of mono and dipyrimidine fragments in mtDNA is more than 30 mole %, whereas in nDNA it does not exceed 23 mole %. 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 a ‘minor’ base (1.5–3.15 mole %) 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-methyl-cytosine content is concerned. In mitochondria and nuclei of rat liver certain DNA methylase activity has been detected, which providesin vitro the methylation of cytosine residues both in homologous DNA and various heterologous DNAs. The specificity of methylationin vitro of cytosine residues in the same heterologous DNA fromE. coli B varies with the source of enzymes. The mitochondrial enzyme methylates cytosine as the lone monopyrimidine residue, whereas the nuclear enzyme methylates cytosine in the di- and tripyrimidine fragments. Ausführliche Beschreibung