Accuracy of Genome Reassembly in γ-Irradiated Escherichia coli

Abstract

γ-Radiation, a powerful DNA-damaging agent, can often lead to the formation of genome rearrangements. In this study, we have assessed the capacity of Escherichia coli to accurately reassemble its genome after multiple double-strand DNA breaks caused by γ-radiation. It has recently been shown that very high doses of γ-radiation or RecA protein deficiency cause erroneous chromosomal assemblies in Deinococcus radiodurans, a highly radiation-resistant bacterium. Accordingly, we have examined the accuracy of genome reassembly in both wild-type and recA strains of E. coli after exposure to the doses of γ-radiation which reduce the survival by 10^6 - to 10^7 -fold. Thirty-eight percent of wild-type survivors showed gross genome changes, most of which were found to be the consequence of the excision of e14, a 15-kb defective prophage. Only one additional type of gross genome rearrangement was detected, presumably representing the duplication of a DNA fragment. These results demonstrate an unexpectedly accurate genome reassembly in wild-type E. coli. We have detected no genome rearrangements in recA recBCD and recA recBCD sbcB mutants, suggesting that RecA-independent DNA repair in E. coli may also be accurate