Accuracy of Genome Reassembly in γ-Irradiated Escherichia coli

Jelena Repar, Davor Zahradka and Ksenija Zahradka*

Department of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia

Article history:
Received September 25, 2012 
Accepted May 22, 2013

Key words:
Escherichia coli, DNA repair, double-strand DNA breaks, genome rearrangements, γ-radiation, recA mutants

Summary:                                                                                                                                                                                 
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 g-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 10⁶- to 10⁷-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.

*Corresponding author:          kvlahovi@irb.hr
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