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DNA-methylase from regenerating rat liver: purification and characterisation
Nucleic Acids Research
|June 1, 1978
Summary
Researchers purified DNA methylase from rat liver, finding it can methylate both single and double-stranded DNA, primarily at CpG sites. This enzyme shows differential substrate preference, methylating bacterial DNA more than rat DNA.
Area of Science:
- Biochemistry
- Molecular Biology
- Epigenetics
Background:
- DNA methylation is a crucial epigenetic mechanism regulating gene expression.
- Understanding DNA methylase activity is key to deciphering epigenetic regulation in various organisms.
Purpose of the Study:
- To purify and characterize DNA methylase from regenerating rat liver.
- To investigate the substrate specificity and methylation patterns of the purified enzyme.
Main Methods:
- Purification of DNA methylase from rat liver nuclei using a 660-fold enrichment.
- Assaying enzyme activity on various DNA substrates, including single-stranded (ss) and double-stranded (ds) DNA, prokaryotic and eukaryotic DNA, synthetic copolymers, and viral DNA (SV40 and PM2).
- Analysis of methylation products and patterns, including methylated pyrimidine isostichs and dinucleotide analysis.
Main Results:
- Purified DNA methylase produces only 5-methylcytosine.
- The enzyme efficiently methylates ssDNA and dsDNA from prokaryotes (M. luteus) and eukaryotes (Ascaris suis), as well as synthetic DNA polymers.
- PM2 DNA is a good substrate, while SV40 DNA is poorly methylated.
- Differential methylation efficiency observed: 1 in 17 bases in M. luteus DNA versus 1 in 590 bases in rat liver DNA.
- Suggests potential for methylation of all CpG sites in DNA.
Conclusions:
- The purified rat liver DNA methylase exhibits broad substrate specificity.
- The enzyme preferentially methylates CpG sites, with significant differences in methylation levels between homologous and heterologous DNA.
- This enzyme plays a role in epigenetic regulation and DNA modification.