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[DNA-methylase activities from animal mitochondria and nuclei: different specificity of DNA methylation]
Abstract:
DNA-methylase activities which methylate cytosine residues in homo- and heterologous DNA were detected in mitochondria and nuclei from rat liver and beef heart. Adenine modifying DNA-methylases in mitochondria and nuclei were not found. DNA from mitochondria and nuclei differ significantly in the methylation degree and in the pattern of the 5-methyl-cytosine distribution by pyrimidine isostichs as DNA in vivo and in vitro being methylated. Mitochondrial DNA methylase has the maximum activity at 30 degrees and pH 7.8 this enzyme(s) differ(s) from the nuclear one(s) in the pH dependence of its activity. After exhaustive in vitro methylation of various DNA by the nuclear enzyme DNA-methylase from mitochondria additionally introduces CH3 groups from S-adenosylmethionine into these DNA (about 3 times more CH3 groups than nuclear enzyme). Nuclear DNA-methylase also methylates DNA which is previously fully-methylated by the mitochondrial enzyme, but to a lesser degree. In conditions of exhaustive DNA methylation mitochondrial enzyme introduces into E. coli B DNA about four times more methyl groups as compared to the nuclear one. After the methylation of E. coli B DNA by mitochondrial enzyme the label (3H-methyl) was detected predominantly in mono-, and in case of nuclear enzyme--in di- and tripyrimidine fragments. Mitochondrial DNA-methylase differs from the nuclear one in the nature of recognized DNA sequences; these enzymes seems to be represented by different proteins. The mitochondrial enzyme methylates shorter nucleotide sequences in DNA as compared to the nuclear DNA-methylase. All these data suggest there exist organoid specificity of genome methylation in animal cell and the modification-restriction systems in animal nucleus and mitochondria are different in character.
Insights
Mitochondria and nuclei possess distinct DNA methylases that modify cytosine residues. These enzymes exhibit differences in activity, methylation patterns, and recognized DNA sequences, suggesting organoid-specific genome methylation in animal cells.
Area of Science:
- Molecular Biology
- Epigenetics
- Cellular Biology
Background:
- DNA methylation is a crucial epigenetic mechanism regulating gene expression.
- Mitochondria and nuclei are key cellular organelles with distinct roles in DNA metabolism.
- Understanding DNA modification in different cellular compartments is vital for comprehending genome regulation.
Purpose of the Study:
- To detect and characterize DNA-methylase activities in mitochondria and nuclei of rat liver and beef heart.
- To compare the properties and substrate specificities of mitochondrial and nuclear DNA methylases.
- To investigate the organoid specificity of genome methylation in animal cells.
Main Methods:
- Detection and assay of DNA-methylase activities in isolated mitochondria and nuclei.
- Methylation of homologous and heterologous DNA using nuclear and mitochondrial enzymes.
- Analysis of methylation degree and distribution patterns of 5-methylcytosine.
- Characterization of enzyme kinetics, including pH and temperature optima.
- Comparative analysis of methylation by mitochondrial and nuclear enzymes on E. coli B DNA.
Main Results:
- DNA-methylase activities were found in both mitochondria and nuclei, methylating cytosine residues.
- Mitochondrial DNA methylase showed optimal activity at 30°C and pH 7.8, differing in pH dependence from nuclear enzymes.
- Mitochondrial DNA methylase introduced significantly more methyl groups into DNA compared to the nuclear enzyme, particularly into shorter nucleotide sequences.
- The distribution patterns of 5-methylcytosine differed between mitochondrial and nuclear DNA methylation.
- Evidence suggests distinct DNA sequence recognition by mitochondrial and nuclear DNA methylases.
Conclusions:
- Mitochondria and nuclei harbor distinct DNA methylases with unique biochemical properties and substrate specificities.
- These findings indicate organoid specificity in genome methylation within animal cells.
- The modification-restriction systems in animal cell mitochondria and nucleus are fundamentally different.