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 w ith X-rays and alpha-particles. After electrophoresis, gels were stain ed with ethidium bromide, placed on a UV-transilluminator and photogra phed with a digitizing camera connected to a personal computer. The pi ctures obtained were processed with the help of specially developed so ftware which allows for the correction of the camera's shading effect and background fluorescence. Linearity between DNA amount and fluoresc ence was demonstrated. Fluorescence intensity for the band with the lo west electrophoretic mobility was found to decrease exponentially with dose. Based on the known size of the native DNA molecules, double-str and 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 Me V Am-241 alpha-particles respectively which gives a relative biologica l effectiveness of 1.8+/-0.1.