A NEW MONOFUNCTIONAL PYRIDOPSORALEN: PHOTOREACTIVITY and REPAIR IN YEAST

Abstract— The newly synthesized derivative of psoralen, the pyrido (3,4-c) 7 methylpsoralen (MePyPs), acts in combination with 365 nm ultraviolet as a monofunctional agent on yeast DNA. In vivo, its photoaffinity for DNA is much higher than that of the bifunctional agent, 8-methoxypsoralen (8-MOP). The MePyPs photo-induced monoadducts are almost completely removed from wild type cells DNA as efficiently as 8-MOP photo-induced adducts during post-treatment incubation. This process is blocked in excision-repair defective mutants (6 to 10% residual excision in radl- Δ or rad2- Δ ). For an equal number of photoinduced lesions, the DNA single strand breaks which are produced concomitantly to MePyPs or 8-MOP photoadducts excision are rapidly rejoined in the case of 8-MOP whereas they are only partly resealed for the MePyPs treatment. The high photo-toxicity of MePyPs, a promising agent for photo-chemotherapeutic use, is explained in terms of the high photoaffinity for DNA.