title: IS-linked movement of a restriction-modification system.
abstract: Potential mobility of restriction-modification systems has been suggested by evolutionary/bioinformatic analysis of prokaryotic genomes. Here we demonstrate in vivo movement of a restriction-modification system within a genome under a laboratory condition. After blocking replication of a temperature-sensitive plasmid carrying a PaeR7I restriction-modification system in Escherichia coli cells, the plasmid was found integrated into the chromosome of the surviving cells. Sequence analysis revealed that, in the majority of products, the restriction-modification system was linked to chromosomal insertion sequences (ISs). Three types of products were: (I) apparent co-integration of the plasmid and the chromosome at a chromosomal IS1 or IS5 copy (24/28 analyzed); (II) de novo insertion of IS1 with the entire plasmid except for a 1-3 bp terminal deletion (2/28); and (III) reciprocal crossing-over between the plasmid and the chromosome involving 1-3 bp of sequence identity (2/28). An R-negative mutation apparently decreased the efficiency of successful integration by two orders of magnitude. Reconstruction experiments demonstrated that the restriction-dependence was mainly due to selection against cells without proper integration: their growth was inhibited by the restriction enzyme action. These results demonstrate collaboration of a mobile element and a restriction-modification system for successful joint migration. This collaboration may have promoted the spread and, therefore, the long-term persistence of these complexes and restriction-modification systems in a wide range of prokaryotes.
authors.affiliation: Laboratory of Social Genome Science, Department of Medical Genome Sciences, Graduate School of Frontier Science, University of Tokyo, Minato-ku, Tokyo, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Takahashi
authors.forename: Seishi
authors.initials: S
authors.lastname: Ohashi
authors.forename: Marat R
authors.initials: MR
authors.lastname: Sadykov
authors.forename: Yoko
authors.initials: Y
authors.lastname: Mizutani-Ui
authors.forename: Ichizo
authors.initials: I
authors.lastname: Kobayashi
mesh_terms: D019295:Computational Biology; D015280:DNA Restriction-Modification Enzymes; D004926:Escherichia coli / Q000235:genetics; D016678:Genome; D016254:Mutagenesis, Insertional; D010957:Plasmids
chemical_list: D015280:DNA Restriction-Modification Enzymes