MOLECULAR MECHANISMS OF DNA-DAMAGE BY LASER-RADIATION

Photoscission of DNA in the presence of ethidium bromide or riboflavin (vitamin BZ) was studied. Laser irradiation of DNA in the presence of these agents induced single- and double-stranded lesions in a superco iled plasmid pBR322. Their formation was monitored by the content of r elaxed and linear forms of the plasmid. The possibility of DNA scissio n al the expense of the energy absorbed by a nonintercalating chromoph ore (riboflavin) was demonstrated for the first time. The dependence o f the number of radiation-induced lesions in the presence of riboflavi n on the energy density in the impulse implies a nonlinear (two-quantu m) mode of photoscission. It was shown that the quantum yield of DNA p hotoscission in the presence of riboflavin is severalfold higher than that for ethidium bromide.