title: Subunit and functional size of human placental DNA methyltransferase involved in de novo and maintenance methylation.
abstract: The subunit molecular size of human DNA methyltransferase isolated from nuclear extracts of placenta was determined on the electroblotted polypeptides after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and compared with the functional size by high performance size exclusion chromatography on Superose 12 and gamma radiation inactivation analysis. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis results indicated a subunit mass of 120 +/- 10 kDa, while the functional size data indicates that the enzyme operates both in de novo and maintenance modes as a dimer of molecular mass 220 +/- 15 kDa with no evidence of monomers in solution of ionic strength between 0.1 and 0.8 M NaCl. The 220-kDa activity carried out the transmethylation of both hemi- and unmethylated DNA substrates. There was no evidence for separate functional catalytic sites on each monomer subunit acting independently when engaged in methylation of hemimethylated or single-stranded DNA from the invariance of radiation inactivation target size with these substrates. The radiation inactivation target size was 230 +/- 15 kDa.
mesh_terms: D004248:DNA (Cytosine-5-)-Methyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008745:Methylation; D008970:Molecular Weight; D010920:Placenta / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D046911:Macromolecular Substances; D004248:DNA (Cytosine-5-)-Methyltransferases