title: Cellular localization and dynamics of the Mrr type IV restriction endonuclease of Escherichia coli.
abstract: In this study, we examined the intracellular whereabouts of Mrr, a cryptic type IV restriction endonuclease of Escherichia coli K12, in response to different conditions. In absence of stimuli triggering its activity, Mrr was found to be strongly associated with the nucleoid as a number of discrete foci, suggesting the presence of Mrr hotspots on the chromosome. Previously established elicitors of Mrr activity, such as exposure to high (hydrostatic) pressure (HP) or expression of the HhaII methyltransferase, both caused nucleoid condensation and an unexpected coalescence of Mrr foci. However, although the resulting Mrr/nucleoid complex was stable when triggered with HhaII, it tended to be only short-lived when elicited with HP. Moreover, HP-mediated activation of Mrr typically led to cellular blebbing, suggesting a link between chromosome and cellular integrity. Interestingly, Mrr variants could be isolated that were specifically compromised in either HhaII- or HP-dependent activation, underscoring a mechanistic difference in the way both triggers activate Mrr. In general, our results reveal that Mrr can take part in complex spatial distributions on the nucleoid and can be engaged in distinct modes of activity.
authors.affiliation: Department of Microbial and Molecular Systems (M2S), Laboratory of Food Microbiology, KU Leuven, B-3001 Leuven, Belgium and Department of Chemistry, KU Leuven, B-3001 Leuven, Belgium.
authors.forename: Anirban
authors.initials: A
authors.lastname: Ghosh
authors.forename: Ioannis
authors.initials: I
authors.lastname: Passaris
authors.forename: Mehari
authors.initials: M
authors.lastname: Tesfazgi Mebrhatu
authors.forename: Susana
authors.initials: S
authors.lastname: Rocha
authors.forename: Kristof
authors.initials: K
authors.lastname: Vanoirbeek
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Abram
authors.initials: A
authors.lastname: Aertsen
mesh_terms: D004262:DNA Restriction Enzymes / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D015263:Deoxyribonucleases, Type III Site-Specific; D029968:Escherichia coli Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D006874:Hydrostatic Pressure; D009154:Mutation
chemical_list: D029968:Escherichia coli Proteins; D004262:DNA Restriction Enzymes; C070141:Mrr protein, E coli; D015252:Deoxyribonucleases, Type II Site-Specific; C032229:GANTC-specific type II deoxyribonucleases; D015263:Deoxyribonucleases, Type III Site-Specific