DNA STRAND BREAKS INDUCED BY RESONANT PHO TOABSORPTION OF PHOSPHORUS ATOMS - A MODEL FOR DIRECT EFFECTS IN RADIOBIOLOGY

Single-strand breaks (ssb) and double-strand breaks (dsb) are induced upon K-shell resonant absorption (2152.4 eV) of phosphorus atoms in DN A. A kinetic analysis allows the determination of the cross sections o f strand breaks production. The quantum yield for ssb induction is equ al to unity, showing that they result from the production of multichar ged centres on phosphorus atoms. The ratio dsb/ssb is equal to 0.09. T his high value is of the order of magnitude of that found for heavy io n irradiations. The dsb production could be due either to electron cap ture on the second strand by the multicharged centres, or by interacti on of the second strand with Auger electrons produced by the electroni c rearrangement of the excited core of the phosphorus atoms.