INDUCTION OF DNA DOUBLE-STRAND BREAKS BY IONIZING-RADIATION AT THE C-MYC LOCUS COMPARED WITH THE WHOLE GENOME - A STUDY USING PULSED-FIELD GEL-ELECTROPHORESIS AND GENE PROBING

Ionizing radiation-induced double-strand breaks (dsb) in a hum;ln colo n carcinoma-derived cell line COLO320HSR were determined from the frag ment size distribution of non-specifically labelled DNA and Sfr I rest riction enzyme-digested DNA uniformly labelled with a c-myc probe. The dose-effect relation for the induction of DNA dsb was linear with no significant difference between slopes for the curves in the whole geno me (7.2 +/- 0.3 x 10(-9) dsb/bp/Gy) and in the 130 kbp restriction fra gments containing c-myc (6.5 +/- 0.5 x 10(-9) dsb/bp/Gy). The size dis tribution of the c-mgc fragments showed deviations from the random-bre akage model, indicating heterogeneity of dsb induction at this locus.