INFLUENCE OF CHROMOSOMAL POSITION AND COPY NUMBER OF A WHITE-DIRECTEDRIBOZYME GENE ON THE SUPPRESSION OF EYE PIGMENTATION IN DROSOPHILA-MELANOGASTER

Different strains of transgenic Drosophila melanogaster carrying one, two, or three copies of a heat-shock pro-meter 70 (hsp70)-driven catal ytic antisense RNA gene, directed against the white gene, were investi gated for the expression level of ribozyme RNA. It was found that the steady-state concentrations of the hammerhead ribozyme were proportion al to the copy number of the genes and that tile suppressive effect on eye pigment accumulation was dosage dependent. In a further experimen t, a D. melanogaster strain, deficient in eye pigmentation caused by a deletion of the white gene, was used for P element-mediated germline transformation: the transposon used contained the hsp70-driven, white- directed ribozyme gene and, on the same DNA, the mini-white gene under its own promoter. The spatial coupling of the transcription of ribozy me and target RNA resulted in more effective ribozyme-mediated inhibit ion of eye pigmentation under heat-shock conditions. These effects wer e dependent on the chromosomal integration site of the transposon.