title: Recognition of unusual DNA structures by human DNA (cytosine-5)methyltransferase.
abstract: The symmetry of the responses of the human DNA (cytosine-5)methyltransferase to alternative placements of 5-methylcytosine in model oligodeoxynucleotide duplexes containing unusual structures has been examined. The results of these experiments more clearly define the DNA recognition specificity of the enzyme. A simple three-nucleotide recognition motif within the CG dinucleotide pair can be identified in each enzymatically methylated duplex. The data can be summarized by numbering the four nucleotides in the dinucleotide pair thus: 1 4/2 3. With reference to this numbering scheme, position 1 can be occupied by cytosine or 5-methylcytosine; position 2 can be occupied by guanosine or inosine; position 3, the site of enzymatic methylation, can be occupied only by cytosine; and position 4 can be occupied by guanosine, inosine, O6-methylguanosine, cytosine, adenosine, an abasic site, or the 3' hydroxyl group at the end of a gapped molecule. Replacing the guanosine normally found at position 4 with any of the moieties introduces unusual (non-Watson-Crick) pairing at position 3 and generally enhances methylation of the cytosine at that site. The exceptional facility of the enzyme in actively methylating unusual DNA structures suggests that the evolution of the DNA methyltransferase, and perhaps DNA methylation itself, may be linked to the biological occurrence of unusual DNA structures.
authors.affiliation: City of Hope Medical Center, Duarte, CA.
authors.forename: S S
authors.initials: SS
authors.lastname: Smith
authors.forename: J L
authors.initials: JL
authors.lastname: Kan
authors.forename: D J
authors.initials: DJ
authors.lastname: Baker
authors.forename: B E
authors.initials: BE
authors.lastname: Kaplan
authors.forename: P
authors.initials: P
authors.lastname: Dembek
mesh_terms: D044503:5-Methylcytosine; D001483:Base Sequence; D003596:Cytosine / Q000031:analogs & derivatives / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D015257:DNA-Cytosine Methylases / Q000378:metabolism*; D015226:Dinucleoside Phosphates / Q000378:metabolism; D005260:Female; D006801:Humans; D008745:Methylation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009692:Nucleic Acid Heteroduplexes
chemical_list: D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; D015257:DNA-Cytosine Methylases; D015226:Dinucleoside Phosphates; D009692:Nucleic Acid Heteroduplexes; C015772:CpG dinucleotide