NEGATIVE REGULATION OF P-ELEMENT EXCISION BY THE SOMATIC PRODUCT AND TERMINAL SEQUENCES OF P IN DROSOPHILA-MELANOGASTER

A transient in vivo P element excision assay was used to test the regulatory properties of putative repressor-encoding plasmids in Drosophila melanogaster embryos. The somatic expression of an unmodified transposase transcription unit under the control of a heat shock gene promoter (phspi) effectively repressed P excision in a dose-dependent manner at very low concentrations relative to somatically active transposase (encoded by the hspiDELTA2-3 gene). Maximum repression required transcription of the complete transposase gene. Dose-dependent repression of P excision was also observed in the presence of a vector plasmid (pCarnegie4) having only the terminal sequences, including transposase binding sites, of the P element. However, repression required considerably higher concentrations of pCarnegie 4 than phspi, and elimination of P excision was not observed.