Ionizing radiation damage to the folded chromosome of Escherichia coli K-12: repair of double-strand breaks in deoxyribonucleic acid.

TitleIonizing radiation damage to the folded chromosome of Escherichia coli K-12: repair of double-strand breaks in deoxyribonucleic acid.
Publication TypeJournal Article
Year of Publication1979
AuthorsUlmer, KM, Gomez, RF, Sinskey, AJ
JournalJ Bacteriol
Volume138
Issue2
Pagination486-91
Date Published1979 May
ISSN0021-9193
KeywordsCell Nucleus, Chromosomes, Bacterial, Cobalt Radioisotopes, DNA Repair, DNA, Bacterial, Escherichia coli, Ribonucleases
Abstract

The extremely gentle lysis and unfolding procedures that have been developed for the isolation of nucleoid deoxyribonucleic acid (DNA; K. M. Ulmer et al., J. Bacteriol. 138:475-485, 1979) yield undamaged, replicating genomes, thus permitting direct measurement of the formation and repair of DNA double-strand breaks at biologically significant doses of ionizing radiation. Repair of ionizing radiation damage to folded chromosomes of Escherichia coli K-12 strain AB2497 was observed within 2 to 3 h of post-irradiation incubation in growth medium. Such behavior was not observed after post-irradiation incubation in growth medium of a recA13 strain (strain AB2487). A model based on recombinational repair is proposed to explain the formation of 2,200 to 2,300S material during early stages of incubation and to explain subsequent changes in the gradient profiles. Association of unrepaired DNA with the plasma membrane is proposed to explain the formation of a peak of rapidly sedimenting material (greater than 3,100S) during the later stages of repair. Direct evidence of repair of double-strand breaks during post-irradiation incubation in growth medium was obtained from gradient profiles of DNA from ribonuclease-digested chromosomes. The sedimentation coefficient of broken molecules was restored to the value of unirradiated DNA after 2 to 3 h of incubation, and the fraction of the DNA repaired in this fashion was equal to the fraction of cells that survived at the same dose. An average of 2.7 double-strand breaks per genome per lethal event was observed, suggesting that one to two double-strand breaks per genome are repairable in E. coli K-12 strain AB2497.

DOI10.1128/jb.138.2.486-491.1979
Alternate JournalJ Bacteriol
Citation Key259
PubMed ID374389
PubMed Central IDPMC218202