The variation in photoreactivating enzyme activity as a function of the stage of growth of three K12 strains of Escherichia coli

Abstract

An investigation of the photoreactivity of the UV-sensitive double mutant K12 AB2480 has indicated that the number of active photoreactivating enzyme molecules is profoundly affected by the physiological state of the cells. This is shown both by the change in repair response of UV-irradiated cells to a single intense flash of light and also by the rate of photoreactivation under conditions of continuous illumination. The cells were found to possess a minimum of active enzyme molecules in exponential phase and a maximum in the late stationary phase. Evidence that this phenomenon is not due to a change in the photoreactivable sector of UV-induced damage is also presented. Further evidence supporting these conclusions is presented with data of the excision-deficient AB1886, and the resistant AB1157 strains.