UV-induced reactivation and mutagenesis of lambda-phages after treatment with 8-methoxypsoralen or thiopyronine and light.

Lesions, which were produced on lambda-phages DNA by the photosensitization effect of 8-methoxypsoralen (8-MOP) can be repaired by UV-induced repair systems (W-reactivation) in Escherichia coli wild type host cells. By optimum induction of the repair system, about 45% of the 8-MOP lesions are repaired. The survival of lambda-phages inactivated by the photodynamic action of thiopyronine (TP) is only negligibly increased by the same UV-induced repair systems. However, the frequencies of clear plaque mutations of 8-MOP treated as well as TP treated lambda-phages increase in similar fashion if the host cells of wild type have been irradiated with UV. These results show the different capacities of induced repair systems in repairing different types of lesions. They also suggest that some types of base damages are repaired more error-prone than other DNA-lesions.