Suppression of gamma ray-induced illegitimate recombination in Escherichia coli by the DNA-binding protein H-NS.
To study the mechanism of gamma-ray-induced illegitimate recombination, we examined the formation of lambdabio transducing phage in Escherichia coli after gamma-ray irradiation. We show that gamma-ray irradiation enhances the formation of lambdabio transducing phage during prophage induction. Moreover, an hns mutation synergistically enhanced the incidence of lambda-ray-induced illegitimate recombination. Next we determined the sequences at the recombination junctions of the lambdabio transducing phages induced by gamma-ray irradiation. Most of the recombination sites coincided with known hotspots. Among them, hotspot I accounted for 67% and 77% of gamma-ray-induced lambdabio transducing phages in the wild type and the hns mutant, respectively. Therefore, the recombination sites appear to occur mostly at hotspot I or at other hotspots, but rarely at non-hotspot sites. These results suggest that types of DNA damage other than the double-strand breaks induced at random sites are mainly responsible for the introduction of the site-specific or region-specific DNA double strand breaks that lead to recombination at the hotspots. The results also showed that the recombination events took place between DNA sequences possessing short stretches of homology. H-NS protein, which binds to curved DNA, suppresses illegitimate recombination in the presence and absence of gamma-ray irradiation. Models for gamma-ray-induced illegitimate recombination are discussed.
Shanado
Y
Y
The Institute of Medical Science, The University of Tokyo, Japan.
Hanada
K
K
Ikeda
H
H
D001426:Bacterial Proteins / Q000378:metabolism*; D010582:Bacteriophage lambda / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000528:radiation effects; D005720:Gamma Rays; D016296:Mutagenesis; D011995:Recombination, Genetic; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria