title: Role of DNA minor groove interactions in substrate recognition by the M.SinI and M.EcoRII DNA (cytosine-5) methyltransferases.
abstract: The SinI and EcoRII DNA methyltransferases recognize sequences (GG(A)/(T)CC and CC(A)/(T)GG, respectively), which are characterized by an (A)/(T) ambiguity. Recognition of the A.T and T.A base pair was studied by in vitro methyltransferase assays using oligonucleotide substrates containing a hypoxanthine.C base pair in the central position of the recognition sequence. Both enzymes methylated the substituted oligonucleotide with an efficiency that was comparable to methylation of the canonical substrate. These observations indicate that M.SinI and M.EcoRII discriminate between their canonical recognition site and the site containing a G.C or a C.G base pair in the center of the recognition sequence (GG(G)/(C)CC and CC(G)/(C)GG, respectively) by interaction(s) in the DNA minor groove. M.SinI mutants displaying a decreased capacity to discriminate between the GG(A)/(T)CC and GG(G)/(C)CC sequences were isolated by random mutagenesis and selection for the relaxed specificity phenotype. These mutations led to amino acid substitutions outside the variable region, previously thought to be the sole determinant of sequence specificity. These observations indicate that (A)/(T) versus (G)/(C) discrimination is mediated by interactions between the large domain of the methyltransferase and the minor groove surface of the DNA.
authors.affiliation: Institute of Biochemistry, Biological Research Center of the Hungarian Academy of Sciences, PO Box 521, Szeged 6701, Hungary. kissa@nucleus.szbk.u-szeged.hu
authors.forename: A
authors.initials: A
authors.lastname: Kiss
authors.forename: G
authors.initials: G
authors.lastname: Pósfai
authors.forename: G
authors.initials: G
authors.lastname: Zsurka
authors.forename: T
authors.initials: T
authors.lastname: Raskó
authors.forename: P
authors.initials: P
authors.lastname: Venetianer
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D015257:DNA-Cytosine Methylases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D019271:Hypoxanthine / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D019271:Hypoxanthine; D004247:DNA; C029528:DNA modification methylase EcoRII; C056154:DNA modification methylase M.SinI; D015257:DNA-Cytosine Methylases