title: Substrate preferences of human placental DNA methyltransferase investigated with synthetic polydeoxynucleotides.
abstract: A DNA methyltransferase partly purified from human placenta has been tested on a variety of synthetic polydeoxynucleotides. The results showed that: the enzyme is most active as a 'maintenance' or 'hemi-' methylase but also has some de novo methylating activity; the presence or absence of A or T in the substrate strand has little influence on maintenance or de novo activity, while polymers containing C but not G in the same strand are poor de novo substrates and bind poorly to the enzyme; single-stranded polymers are about as good substrates as double-stranded ones, and the effects of nucleotide composition (particularly G and mC content) on enzyme activity with single strands are similar to those with double-stranded polymers; strands in which all the cytosines are methylated bind the enzyme well. A mechanism is suggested involving two different sites on the enzyme that recognize CG and mCG, and which rationalizes the activity of eukaryotic DNA methyltransferases towards single-stranded DNA.
mesh_terms: D004247:DNA / Q000138:chemical synthesis / Q000378:metabolism; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000138:chemical synthesis / Q000378:metabolism; D005260:Female; D006801:Humans; D008745:Methylation; D008837:Micrococcus; D009690:Nucleic Acid Conformation; D010920:Placenta / Q000201:enzymology*; D011089:Polydeoxyribonucleotides / Q000138:chemical synthesis / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D011089:Polydeoxyribonucleotides; D004247:DNA; D004248:DNA (Cytosine-5-)-Methyltransferases