Characterization and zeste reaction of spontaneously reduced transposable elements in Drosophila melanogaster

Seven transposable elements (TE), selected from parental stock w 239 Cy, have been characterized. They all carry w+ but have lost both rst+ and the two polytene chromosome bands of a complete TE and are thus cytologically invisible. In situ hybridization with probes from the white-roughest interval shows that the reduced TE's are truncated in the same region, 40-90 kb upstream of the white locus, well proximal to the zeste interaction site. They express the white gene in wild type fashion in all tissues studied (eyes, testis sheaths, and Malpighian tubules) but give zeste reactions varying from yellow to bright red. Thus, by the criterion of the zeste reaction, 40 kb of TE sequences 5' to the transcription start site cannot insulate the white gene from position effects. One single spontaneously reduced TE (TE203) originated from parental stock w TE100 ct. This TE is truncated closer to the white locus (+ 18- +26 kb), but still well separated from the zeste interaction site. In a z1w11E4 background, homozygous TE203 flies have an uneven eye pigmentation, while heterozygotes have eyes that are yellowish red. The Malpighian tubules and testes show wild type pigmentation in both cases, like normal TE's.