Interaction between Ultraviolet Light and y-Radiation Damage in the Induction of Mutants of Escherichia coli: the Effect of Some Modifying Treatments

The effect of various modifying agents has been studied on the synergistic interaction of u.v.- and y-radiation in the induction of prototrophic revertants of tryptophan-requiring Escherichia coli B/r W P 2. The component of y-radia-tion damage involved in the interaction shows a large effect of oxygen during irradiation (dose modifying factor of up to 3) and is thus more like lethal than mutational damage. The interaction mutants respond to various post-irradiation treatments in the same way as u.v.-induced, but not y-induced, mutants, i.e. they are photoreactivable, their frequency is increased by acri-flavine and nutrient broth after irradiation and they are susceptible to mutation frequency decline in minimal medium. It is postulated that damage induced in DNA by y-radiation inhibits the repair of premutational lesions induced by U.V. thus increasing the yield of u.v.-induced mutants. The possible nature of the system involved in this repair (which is not that respon-sible for the excision of thymine dimers from DNA) is discussed