title: Preferential site-specific hemimethylation of GATC sites in pBR322 DNA by Dam methyltransferase from Escherichia coli.
abstract: The methylation pattern of the 22 GATC sites of pBR322 (dam-) by Dam methyltransferase from Escherichia coli has been studied. Preferential hemimethylation took place at positions 3042 and 349. It was found that these preferential methylations were the same in supercoiled circular and linear DNAs. The flanking regions of these preferentially methylated sites contain three G.C pairs on one side and two A.T pairs and one G.C pair on the other. This preferential methylation was confirmed on a 126-base pair oligonucleotide containing two GATC sites with different flanking sequences. The next sites methylated were, in both cases, the first GATC site on the A.T-rich side, although the orientation was different. The rapid methylation of a second and third neighboring GATC site on the same plasmid suggests a processive mechanism. The implications of the orientation of hemimethylation are discussed in the context of the recognition of a palindromic target site by a monomeric DNA-binding protein.
authors.affiliation: Département de Biologie, Centre d'Etudes Nucléairs de Saclay, Gif-sur-Yvette, France.
authors.forename: A
authors.initials: A
authors.lastname: Bergerat
authors.forename: A
authors.initials: A
authors.lastname: Kriebardis
authors.forename: W
authors.initials: W
authors.lastname: Guschlbauer
mesh_terms: D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D004278:DNA, Superhelical / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D066298:In Vitro Techniques; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D010957:Plasmids; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D004269:DNA, Bacterial; D004278:DNA, Superhelical; D029968:Escherichia coli Proteins; D008780:Methyltransferases; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499294:dam protein, E coli