title: A ΔdinB mutation that sensitizes Escherichia coli to the lethal effects of UV- and X-radiation.
abstract: The DinB (PolIV) protein of Escherichia coli participates in several cellular functions. We investigated a dinB mutation, Δ(dinB-yafN)883(::kan) [referred to as ΔdinB883], which strongly sensitized E. coli cells to both UV- and X-radiation killing. Earlier reports indicated dinB mutations had no obvious effect on UV radiation sensitivity which we confirmed by showing that normal UV radiation sensitivity is conferred by the ΔdinB749 allele. Compared to a wild-type strain, the ΔdinB883 mutant was most sensitive (160-fold) in early to mid-logarithmic growth phase and much less sensitive (twofold) in late log or stationary phases, thus showing a growth phase-dependence for UV radiation sensitivity. This sensitizing effect of ΔdinB883 is assumed to be completely dependent upon the presence of UmuDC protein; since the ΔdinB883 mutation did not sensitize the ΔumuDC strain to UV radiation killing throughout log phase and early stationary phase growth. The DNA damage checkpoint activity of UmuDC was clearly affected by ΔdinB883 as shown by testing a umuC104 ΔdinB883 double-mutant. The sensitivities of the ΔumuDC strain and the ΔdinB883 ΔumuDC double-mutant strain were significantly greater than for the ΔdinB883 strain, suggesting that the ΔdinB883 allele only partially suppresses UmuDC activity. The ΔdinB883 mutation partially sensitized (fivefold) uvrA and uvrB strains to UV radiation, but did not sensitize a ΔrecA strain. A comparison of the DNA sequences of the ΔdinB883 allele with the sequences of the Δ(dinB-yafN)882(::kan) and ΔdinB749 alleles, which do not sensitize cells to UV radiation, revealed ΔdinB883 is likely a "gain-of-function" mutation. The ΔdinB883 allele encodes the first 54 amino acids of wild-type DinB followed by 29 predicted residues resulting from the continuation of the dinB reading frame into an adjacent insertion fragment. The resulting polypeptide is proposed to interfere directly or indirectly with UmuDC function(s) involved in protecting cells against the lethal effects of radiation.
authors.affiliation: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA.
authors.forename: Mei-Chong W
authors.initials: MC
authors.lastname: Lee
authors.affiliation: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Franco
authors.affiliation: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA.
authors.forename: Doris M
authors.initials: DM
authors.lastname: Vargas
authors.affiliation: Department of Microbiology and Immunology, A.T. Still University, Kirksville College of Osteopathic Medicine, Kirksville, MO 63501, USA.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Hudman
authors.affiliation: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: White
authors.affiliation: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA. Electronic address: rfowler@sjsu.edu.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Fowler
authors.affiliation: Department of Microbiology and Immunology, A.T. Still University, Kirksville College of Osteopathic Medicine, Kirksville, MO 63501, USA.
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Sargentini
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000483:Alleles; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D050296:Microbial Viability / Q000235:genetics / Q000528:radiation effects; D009154:Mutation; D014466:Ultraviolet Rays; D014965:X-Rays
chemical_list: D004268:DNA-Binding Proteins; C094399:DinB protein, E coli; D029968:Escherichia coli Proteins; C058093:UvrB protein, E coli; C078202:UmuC protein, E coli; D004259:DNA-Directed DNA Polymerase; C055218:UmuD protein, E coli; C068631:UvrA protein, E coli; D000251:Adenosine Triphosphatases; D004265:DNA Helicases
keywords: Checkpoint; DinB; Escherichia coli; TLS; UV radiation sensitivity; UmuDC