title: Escherichia coli K-12 restricts DNA containing 5-methylcytosine.
abstract: We have observed that plasmids containing certain cloned modification methylase genes of type II restriction-modification systems cannot be transformed into many laboratory strains of Escherichia coli K-12. The investigation of this phenomenon, reported here, has revealed (i) DNA containing 5-methylcytosine is biologically restricted by these strains, while DNA containing 6-methyladenine is not; (ii) restriction is due to two genetically distinct systems that differ in their sequence specificities, which we have named mcrA and mcrB (for modified cytosine restriction). Since 5-methylcytosine containing DNA is widespread in nature, the Mcr systems probably have a broad biological role. Mcr restriction may seriously interfere with molecular cloning of 5-methylcytosine-containing foreign DNAs. The Mcr phenotypes of some commonly used strains of E. coli K-12 are reported.
mesh_terms: D044503:5-Methylcytosine; D010582:Bacteriophage lambda; D001483:Base Sequence; D003001:Cloning, Molecular / Q000379:methods*; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism; D004262:DNA Restriction Enzymes / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial; D008780:Methyltransferases / Q000235:genetics*; D010641:Phenotype; D013379:Substrate Specificity
chemical_list: D044503:5-Methylcytosine; D003596:Cytosine; D008780:Methyltransferases; D004262:DNA Restriction Enzymes