title: Novel non-specific DNA adenine methyltransferases.
abstract: The mom gene of bacteriophage Mu encodes an enzyme that converts adenine to N(6)-(1-acetamido)-adenine in the phage DNA and thereby protects the viral genome from cleavage by a wide variety of restriction endonucleases. Mu-like prophage sequences present in Haemophilus influenzae Rd (FluMu), Neisseria meningitidis type A strain Z2491 (Pnme1) and H. influenzae biotype aegyptius ATCC 11116 do not possess a Mom-encoding gene. Instead, at the position occupied by mom in Mu they carry an unrelated gene that encodes a protein with homology to DNA adenine N(6)-methyltransferases (hin1523, nma1821, hia5, respectively). Products of the hin1523, hia5 and nma1821 genes modify adenine residues to N(6)-methyladenine, both in vitro and in vivo. All of these enzymes catalyzed extensive DNA methylation; most notably the Hia5 protein caused the methylation of 61% of the adenines in λ DNA. Kinetic analysis of oligonucleotide methylation suggests that all adenine residues in DNA, with the possible exception of poly(A)-tracts, constitute substrates for the Hia5 and Hin1523 enzymes. Their potential 'sequence specificity' could be summarized as AB or BA (where B = C, G or T). Plasmid DNA isolated from Escherichia coli cells overexpressing these novel DNA methyltransferases was resistant to cleavage by many restriction enzymes sensitive to adenine methylation.
authors.affiliation: Department of Virology, Institute of Microbiology, Faculty of Biology, University of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Drozdz
authors.forename: Andrzej
authors.initials: A
authors.lastname: Piekarowicz
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: Monika
authors.initials: M
authors.lastname: Radlinska
mesh_terms: D000225:Adenine / Q000378:metabolism*; D010583:Bacteriophage mu / Q000235:genetics; D001483:Base Sequence; D019175:DNA Methylation; D004262:DNA Restriction Enzymes / Q000378:metabolism; D006193:Haemophilus influenzae / Q000235:genetics; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D023282:Nuclease Protection Assays; D039002:Prophages / Q000201:enzymology* / Q000235:genetics; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000737:chemistry / Q000235:genetics; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D014764:Viral Proteins; D008780:Methyltransferases; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D004262:DNA Restriction Enzymes; D000225:Adenine
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