title: Identification of a second polypeptide required for McrB restriction of 5-methylcytosine-containing DNA in Escherichia coli K12.
abstract: The McrB restriction system in Escherichia coli K12 causes sequence-specific recognition and inactivation of DNA containing 5-methylcytosine residues. We have previously located the mcrB gene near hsdS at 99 min on the E. coli chromosome and demonstrated that it encodes a 51 kDa polypeptide required for restriction of M.AluI methylated (A-G-5mC-T) DNA. We show here, by analysis of maxicell protein synthesis of various cloned fragments from the mcrB region, that a second protein of approximately 39 kDa is also required for McrB-directed restriction. The new gene, designated mcrC, is adjacent to mcrB and located distally to hsdS. The McrB phenotype has been correlated previously with restriction of 5-hydroxy-methyl-cytosine (HMC)-containing T-even phage DNA that lacks the normal glucose modification of HMC, formally designated RglB (for restriction of glucoseless phage). This report reveals a difference between the previously correlated McrB and RglB restriction systems: while both require the mcrB gene product only the McrB system requires the newly identified mcrC-encoded 39-kDa polypeptide.
authors.affiliation: Department of Microbiology, Louisiana State University, Baton Rouge 70803.
authors.forename: T K
authors.initials: TK
authors.lastname: Ross
authors.forename: E C
authors.initials: EC
authors.lastname: Achberger
authors.forename: H D
authors.initials: HD
authors.lastname: Braymer
mesh_terms: D044503:5-Methylcytosine; D003596:Cytosine / Q000031:analogs & derivatives / Q000378:metabolism; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D010641:Phenotype; D010957:Plasmids
chemical_list: D015280:DNA Restriction-Modification Enzymes; D004269:DNA, Bacterial; D044503:5-Methylcytosine; D003596:Cytosine