FORMATION OF CYCLOBUTANE THYMINE DIMERS FROM UVA PHOTOSENSITIZATION OF PYRIDOPSORALEN MONOADDUCTED DNA

The present report provides evidence that thymine dimerization can be UVA photosensitized at a tetranucleotide, 5'-TATT-3', by a 7-methyl-py rido(3,4-c)psoralen monoadduct in DNA. The efficiency of the photoproc ess depends on the tetranucleotide flanking sequences. These results d emonstrate that one DNA lesion can originate the contiguous formation of a second type of lesion and emphasize the sequence-specific respons e to interaction of drugs with DNA. Results are related to the sensiti vity of DNA to 1,10-phenanthroline-cuprous ion complex nucleolytic act ivity and discussed in terms of the major role of local deformability of DNA in interaction with ligands.