title: Quick replication fork stop by overproduction of Escherichia coli DinB produces non-proliferative cells with an aberrant chromosome.
abstract: Escherichia coli dinB encodes the translesion DNA polymerase DinB, which can inhibit progression of replication forks in a dose-dependent manner, independent of exogenous DNA damage. We reported previously that overproduction of DinB from a multicopy dinB plasmid immediately abolished ongoing replication fork progression, and the cells rapidly and drastically lost colony-forming ability, although the mechanisms underlying this lethality by severe replication fork stress remained unclear. Here, we show that the reduced colony-forming ability in the dinB-overexpressing cells is independent of the specific toxin genes that trigger programmed bacterial cell death when replication is blocked by depletion of the dNTP pool. After DinB abolished replication fork progression and colony-forming ability, most of the cells were still viable, as judged by fluorescent dye staining, but contained irregularly shaped nucleoids in which chromosomal DNA was preferentially lost in the replication terminus region relative to the replication origin region. Flow cytometric analysis of the cells revealed chromosomal damage and the eventual appearance of cell populations with less than single-chromosome DNA content, reminiscent of sub-G1 cells with lethal DNA content produced during eukaryotic apoptosis. This reduced DNA content was not observed after replication fork progression was quickly stopped in temperature-sensitive dnaB helicase mutant cells at a non-permissive temperature. Thus, the quick replication stop provoked by excess DinB uniquely generates temporarily viable but non-reproductive cells possessing a fatally depleted chromosomal content, which may represent one of the possible fates of an E. coli cell whose replication is overwhelmingly compromised.
authors.affiliation: Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 　Takayama,Ikoma, Nara 630-0192, Japan.
authors.forename: Mio
authors.initials: M
authors.lastname: Ikeda
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shinozaki
authors.forename: Kaori
authors.initials: K
authors.lastname: Uchida
authors.forename: Yasuha
authors.initials: Y
authors.lastname: Ohshika
authors.forename: Asako
authors.initials: A
authors.lastname: Furukohri
authors.forename: Hisaji
authors.initials: H
authors.lastname: Maki
authors.forename: Masahiro Tatsumi
authors.initials: MT
authors.lastname: Akiyama
mesh_terms: D016923:Cell Death; D049109:Cell Proliferation; D002869:Chromosome Aberrations; D004261:DNA Replication; D053488:DnaB Helicases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D018741:Replication Origin; D015854:Up-Regulation
chemical_list: C094399:DinB protein, E coli; D029968:Escherichia coli Proteins; D009711:Nucleotides; D053488:DnaB Helicases