title: Multiplication of a restriction-modification gene complex.
abstract: Previous works have suggested that some gene complexes encoding a restriction (R) enzyme and a cognate modification (M) enzyme may behave as selfish mobile genetic elements. RM gene complexes, which destroy 'non-self' elements marked by the absence of proper methylation, are often associated with mobile genetic elements and are involved in various genome rearrangements. Here, we found amplification of a restriction-modification gene complex. BamHI gene complex inserted into the Bacillus chromosome showed resistance to replacement by a homologous stretch of DNA. Some cells became transformed with the donor without losing BamHI. In most of these transformants, multiple copies of BamHI and the donor allele were arranged as tandem repeats. When a clone carrying one copy of each allele was propagated, extensive amplification of BamHI and the donor unit was observed in a manner dependent on restriction enzyme gene. This suggests that restriction cutting of the genome participates in the amplification. Visualization by fluorescent in situ hybridization revealed that the amplification occurred in single cells in a burst-like fashion that is reminiscent of induction of provirus replication. The multiplication ability in a bacterium with natural capacity for DNA release, uptake and transformation will be discussed in relation to spreading of RM gene -complexes.
authors.affiliation: Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Marat
authors.initials: M
authors.lastname: Sadykov
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Asami
authors.forename: Hironori
authors.initials: H
authors.lastname: Niki
authors.forename: Naofumi
authors.initials: N
authors.lastname: Handa
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Itaya
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Ichizo
authors.initials: I
authors.lastname: Kobayashi
mesh_terms: D001407:Bacillus / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002876:Chromosomes, Bacterial; D015280:DNA Restriction-Modification Enzymes; D005784:Gene Amplification; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D017404:In Situ Hybridization, Fluorescence; D016254:Mutagenesis, Insertional; D014170:Transformation, Genetic
chemical_list: D001426:Bacterial Proteins; D015280:DNA Restriction-Modification Enzymes