REPAIR OF 8-METHOXYPSORALEN INDUCED DNA INTERSTRAND CROSS-LINKS IN Tetrahymena thermophila

Abstract— The protozoan Tetrahymena thermophila was treated with 8-methoxypsoralen in combination with long wavelength ultraviolet irradiation and the DNA-repair response was studied. Following the treatment a lag-period in cell proliferation was observed, the duration of which was proportional to the amount of psoralen used, and both swelling and deformation of the cells were observed. The treatment with 3 μg 8-methoxypsoralen/mℓ and a light dose of 8 kJ m^-2 resulted in a 10-fold decrease in DNA and RNA synthesis activity, while the protein synthesis was only moderately affected. Using the same conditions the lag-period was 30 h, and during this time the psoralen induced DNA interstrand cross-links were removed. Alkaline elution experiments showed that the repair process involves DNA single strand scissions, whereas no double strand DNA scissions were detected.