MUTAGENIC and RECOMBINOGENIC EFFECTS OF DNA CROSS-LINKS INDUCED IN YEAST BY 8-METHOXYPSORALEN PHOTOADDITION

— A re-irradiation with a saturating dose of UVA after pretreatment with 8-methoxypsoralen (8-MOP) plus low doses of UVA and removal of unbound 8-MOP, induces an increase in frequencies of mutants and recombinants in repair-proficient Saccharomyces cerevisiae. The magnitude of this increase is proportional to the first UVA dose. An incubation of cells between the two UVA doses allowing the repair of monoadducts produced by the first dose abolishes the enhancement in frequencies of mutants and recombinants. It is concluded that in yeast cross-links are not solely lethal but could constitute, in repair proficient cells, premutagenic and prerecombinogenic lesions.