The introduction includes a review of the recent work on the repair of damage induced in the DNA of bacterial cells by U.V. particular emphasis has been placed on a consideration of the photoenzymatic repair system and on the way recent findings have been used to postulate mechanisms for the repair processes. The experimental work is in two parts. The first section is concerned with experiments undertaken with stationary phase cells of Escherichia coli K12.AB2480 and AB1886. The cells were used to study the kinetics of photoreactivation. Survival curves, with samples at a minimum of six U.V. doses were obtained at several periods of photoreactivation ranging from zero to maximum, and the results were analysed mathematically on the basis of two different repair models. Experiments at different temperatures and dose-rates indicated two distinct rates of photoreactivation. The second experimental section is concerned with an investigation of the different rate processes using the U.V. sensitive AB2480 grown in liquid culture. An initial fast rate could be eliminated by administering a single high intensity light flash at the start of continuous illumination. This experimental technique allowed the recognition of two separate rates during continuous illumination and the dose-rate and temperature dependence of these were characterised. The effect of growth stage on the U.V. sensitivity of AB2480 was also investigated. The results suggest that the number of active repair enzymes per cell changes during the growth cycle. Findings from these experiments have been discussed in relation to the current concepts regarding molecular repair phenomena.
|Date of Award||1971|