RôLE OF DNA REPAIR MECHANISMS IN MICROBIAL INACTIVATION AND RECOVERY PHENOMENA1

Summary We have described what appears to be the major cause of death in bacteria treated with ultraviolet light, X‐rays or nitrogen mustard (HN2): all of these agents produce structural defects in DNA which, unless repaired, are likely to inhibit DNA synthesis or cause some error in protein synthesis, which leads to cell death. Thus, survival is determined by the net probability that these defects either persist and prove lethal, or are repaired after irradiation during the first few hours of incubation on the plating medium. The apparent correlations of u.v., X‐ray and HN2 sensitivity with DNA base composition suggest that the relevant damage caused by these agents is associated with adenine‐thymine base pairs for u.v. and guanine.