title: Endonucleolytic incision of x-irradiated deoxyribonucleic acid by extracts of Escherichia coli.
abstract: An enconuclease activity that reacts with x-irradiated DNA is present in extracts of E. coli. By using centrifugal methods to monitor the conversion of the supercoiled, circular double-stranded DNA for phage phi-x-174 (replicative form) or PM2 to the relaxed circular form it was possible to quantitate the rate of radiation induced endonuclease-sensitive sites in the DNA. For every single-strand break induced by x-rays under aerobic irradiation conditions, there is approximately one induced site sensitive to this endonuclease activity. Under irradiation conditions (addition OF Potassium iodide) that dramatically reduce rates of single-strand breaks and "alkalilabile" lesions, the number of endonuclease-sensitive sites relative to single-strand breaks increase approximatley 4-fold. This nuclease is present in several strains of E. coli B and K12, including mutants deficient in DNA polymerase I, recombination gene products (rec mutants), ultraviolet light incision enzyme (uvr A mutant), and endonuclease II. It is suggested that this endonuclease may be involved in an excision repair process for damages incurred in DNA by ionizing radiation.
mesh_terms: D002499:Centrifugation, Density Gradient; D003090:Coliphages; D004260:DNA Repair; D004270:DNA, Circular / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism / Q000528:radiation effects; D004720:Endonucleases; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D005827:Genetics, Microbial; D007700:Kinetics; D009154:Mutation; D011549:Pseudomonas; D011830:Radiation Effects; D014466:Ultraviolet Rays
chemical_list: D004270:DNA, Circular; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D004720:Endonucleases