P element excision in Drosophila is stimulated by gamma-irradiation in transient embryonic assays.

The influence of gamma-irradiation on P element excision and excision-site repair mechanisms was directly tested by embryonic somatic excision assays. Preblastoderm P[ry+, delta 2-3](99B) embryos, having a stable source of somatically active P transposase, were irradiated previous to injection with P excision indicator plasmids. Frequencies of precise or nearly precise P excision increased with gamma-ray doses ranging from 0.5 to 3.5 Gy. Higher doses resulted in frequencies close to that in unirradiated embryos, though considerable embryonic lethality was also evident at these doses. A direct positive interaction between gamma-irradiation and P element activity is concluded.