title: Evidence for an evolutionary antagonism between Mrr and Type III modification systems.
abstract: The Mrr protein of Escherichia coli is a laterally acquired Type IV restriction endonuclease with specificity for methylated DNA. While Mrr nuclease activity can be elicited by high-pressure stress in E. coli MG1655, its (over)expression per se does not confer any obvious toxicity. In this study, however, we discovered that Mrr of E. coli MG1655 causes distinct genotoxicity when expressed in Salmonella typhimurium LT2. Genetic screening enabled us to contribute this toxicity entirely to the presence of the endogenous Type III restriction modification system (StyLTI) of S. typhimurium LT2. The StyLTI system consists of the Mod DNA methyltransferase and the Res restriction endonuclease, and we revealed that expression of the LT2 mod gene was sufficient to trigger Mrr activity in E. coli MG1655. Moreover, we could demonstrate that horizontal acquisition of the MG1655 mrr locus can drive the loss of endogenous Mod functionality present in S. typhimurium LT2 and E. coli ED1a, and observed a strong anti-correlation between close homologues of MG1655 mrr and LT2 mod in the genome database. This apparent evolutionary antagonism is further discussed in the light of a possible role for Mrr as defense mechanism against the establishment of epigenetic regulation by foreign DNA methyltransferases.
authors.affiliation: Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre, Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.
authors.forename: Mehari
authors.initials: M
authors.lastname: Tesfazgi Mebrhatu
authors.forename: Ewa
authors.initials: E
authors.lastname: Wywial
authors.forename: Anirban
authors.initials: A
authors.lastname: Ghosh
authors.forename: Chris W
authors.initials: CW
authors.lastname: Michiels
authors.forename: Ariel B
authors.initials: AB
authors.lastname: Lindner
authors.forename: François
authors.initials: F
authors.lastname: Taddei
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: Laurence
authors.initials: L
authors.lastname: Van Melderen
authors.forename: Abram
authors.initials: A
authors.lastname: Aertsen
mesh_terms: D015254:DNA Modification Methylases / Q000378:metabolism; D004262:DNA Restriction Enzymes / Q000235:genetics / Q000378:metabolism*; D015263:Deoxyribonucleases, Type III Site-Specific / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D012486:Salmonella typhimurium / Q000201:enzymology / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D015254:DNA Modification Methylases; D004262:DNA Restriction Enzymes; C070141:Mrr protein, E coli; D015263:Deoxyribonucleases, Type III Site-Specific