DNA DOUBLE-STRAND BREAK INDUCTION IN YEAST BY X-RAYS AND ALPHA-PARTICLES MEASURED BY PULSED-FIELD GEL-ELECTROPHORESIS

Pulsed-field gel electrophoresis was used to separate the chromosomes of the diploid yeast Saccharomyces cerevisiae 211B after irradiation with X-rays and alpha-particles. After electrophoresis, gels were stained with ethidium bromide, placed on a UV-transilluminator and photographed with a digitizing camera connected to a personal computer. The pictures obtained were processed with the help of specially developed software which allows for the correction of the camera's shading effect and background fluorescence. Linearity between DNA amount and fluorescence was demonstrated. Fluorescence intensity for the band with the lowest electrophoretic mobility was found to decrease exponentially with dose. Based on the known size of the native DNA molecules, double-strand break yields could be calculated. These were found to be (8.2+/-0.4) and (14.8+/-0.5)10(-12) (g/mol)-1 Gy-1 for 80 keV X-rays and 3.5 MeV Am-241 alpha-particles respectively which gives a relative biological effectiveness of 1.8+/-0.1.