A ?dinB 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, ?(dinB-yafN)883(::kan) [referred to as ?dinB883], 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 ?dinB749 allele. Compared to a wild-type strain, the ?dinB883 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 ?dinB883 is assumed to be completely dependent upon the presence of UmuDC protein; since the ?dinB883 mutation did not sensitize the ?umuDC strain to UV radiation killing throughout log phase and early stationary phase growth. The DNA damage checkpoint activity of UmuDC was clearly affected by ?dinB883 as shown by testing a umuC104 ?dinB883 double-mutant. The sensitivities of the ?umuDC strain and the ?dinB883 ?umuDC double-mutant strain were significantly greater than for the ?dinB883 strain, suggesting that the ?dinB883 allele only partially suppresses UmuDC activity. The ?dinB883 mutation partially sensitized (fivefold) uvrA and uvrB strains to UV radiation, but did not sensitize a ?recA strain. A comparison of the DNA sequences of the ?dinB883 allele with the sequences of the ?(dinB-yafN)882(::kan) and ?dinB749 alleles, which do not sensitize cells to UV radiation, revealed ?dinB883 is likely a "gain-of-function" mutation. The ?dinB883 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.

SUBMITTER: Lee MC 

PROVIDER: S-EPMC4172556 | biostudies-literature | 2014 May-Jun

REPOSITORIES: biostudies-literature