P-element repression in Drosophila melanogaster by a naturally occurring defective telomeric P copy

In Drosophila melanogaster hybrid dysgenesis occurs in progeny from crosses between females lacking P elements and males carrying P elements scattered throughout the genome. We have genetically isolated a naturally occurring P insertion at cytological location 1A, from a Tunisian population. The Nas r'Allah-P(1A) clement [NA-P(1A)] has a deletion of the first 871 bp includi ng the;P promoter. It is flanked at the 3' end by telomeric associated sequ ences and at the 5' end by a HeT-A element sequence. The NA-P(1A) element s trongly represses dysgenic sterility and P transposition. However, when tes ting P-promoter repression, NA-P(1A) was unable to repress a germinally exp ressed P-lacZ construct bearing no 5'-homology with it. Conversely, a secon d P-lacZ construct, in which the fusion with lacZ takes place in exon 3 of P, was successfully repressed by NA-P(1A). This suggests that NA-P(1A) repr ession involves a homology dependent component.