title: Characterization of a unique methyl-specific restriction system in Streptomyces avermitilis.
abstract: Streptomyces avermitilis contains a unique restriction system that restricts plasmid DNA containing N6-methyladenine or 5-methylcytosine. Shuttle vectors isolated from Escherichia coli RR1 or plasmids isolated from modification-proficient Streptomyces spp. cannot be directly introduced into S. avermitilis. This restriction barrier can be overcome by first transferring plasmids into Streptomyces lividans or a modification-deficient E. coli strain and then into S. avermitilis. The transformation frequency was reduced greater than 1,000-fold when plasmid DNA was modified by dam or TaqI methylases to contain N6-methyladenine or by AluI, HhaI, HphI methylases to contain 5-methylcytosine. Methyl-specific restriction appears to be common in Streptomyces spp., since either N6-methyladenine-specific or 5-methylcytosine-specific restriction was observed in seven of nine strains tested.
authors.affiliation: Exploratory Microbiology and Genetics, Merck Sharp & Dohme Research Laboratories, Rahway, New Jersey 07065.
authors.forename: D J
authors.initials: DJ
authors.lastname: MacNeil
mesh_terms: D044503:5-Methylcytosine; D000225:Adenine / Q000031:analogs & derivatives; D003596:Cytosine / Q000031:analogs & derivatives; D004274:DNA, Recombinant / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005822:Genetic Vectors; D008745:Methylation; D010957:Plasmids; D011815:R Factors; D015183:Restriction Mapping; D013302:Streptomyces / Q000235:genetics*
chemical_list: D044503:5-Methylcytosine; D000225:Adenine; D003596:Cytosine; D004274:DNA, Recombinant; C000730567:6-methyladenine