DNA RADIOLYSIS - MAPPING OF THE GENE-REGULATION DOMAINS

Ionizing radiations induce strand breaks and modifications of nucleoti des (base and/or sugar) in DNA. In aerated solution, the damages are m ainly due to the attack of DNA by the hydroxyl radicals (OH .) issued from the radiolysis of water. The lesions occur at every nucleotides a long the DNA molecule. For gamma-rays, beta-rays and fast neutrons, we have determined at each nucleotide the probability of strand breakage at neutral pH and the probability of base and sugar modification lead ing also to strand breakage after an alkaline treatment. The method of sequencing gel electrophoresis was used for this purpose. We have sho wn that the probability of getting a radiation induced damage at a giv en nucleotide is modulated by: i) the chemical nature of this nucleoti de, ii) the local conformation determined by the sequence of nucleotid es and by DNA strandedness (single or double stranded), iii) the type of structure to which the nucleotide belongs (right-handed B- or left- handed Z-DNA) and iv) the presence of proteins specifically (e.g. repr essors) or nonspecifically (histones or histone-like) bound to DNA. Th erefore, radiolysis may be a convenient tool for mapping gene regulati on domains in which DNA is often in non-canonical B forms or is in int eraction with regulatory proteins.