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 excisi on assays. Preblastoderm P[ry(+), Delta 2-3](99B) embryos, having a st able source of somatically active P transposase, were irradiated previ ous to injection with P excision indicator plasmids. Frequencies of pr ecise or nearly precise P excision increased with gamma-ray doses rang ing 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.