A NEW MONOFUNCTIONAL PYRIDOPSORALEN: PHOTOREACTIVITY and REPAIR IN YEAST

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Abstract
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.

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