CHARACTERISTICS OF ENZYMATIC BREAKDOWN OF DNA IN ESCHERICHIA COLI IN RESPONSE TO IONIZING RADIATION

The temperature dependence of DNA degradation has been characterized in E. coli Bs-1 and an activation energy of 17·2 kcal/mole determined for the enzyme function between 20°c and 40°c. The maximum rate of the breakdown function was measured to be near 42°c. At temperatures greater than 45°c heat inactivation of the enzyme system in vivo is evidenced. The dependence of DNA degradation at 37°c on radiation dose has been measured. The radiation appears to produce substrate for the degradative enzyme system, which is present in the cells as normal constituents of the cells. The Michaelis rate constant for such an enzyme reaction would be equivalent to a substrate concentration produced by 8·5 krads irradiation. The buoyant density of DNA throughout the degradative process was measured and found to be the same as double-stranded DNA from unirradiated cells. Models involving the in vitro mechanisms of actions of exonucleases I, II and III predict that a single-stranded component of the DNA should exist. This single-stranded component has not been observed. © 1969 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.