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Chloramphenicol acetyl transferase reporter plasmids driven by the Drosophila ras2/rop promoter were injected into Xenopus oocytes to study Dras2 and rop gene regulation by their bidirectional promoter. When injected without Drosophila nuclear extract, both Dras2 and rep were highly expressed. Dras2 and rop-CAT expression was very similar in Drosophila cells and Xenopus oocytes, suggesting the conservation of regulatory factors between the two species. When Drosophila nuclear extract was co-injected with Dras2 and rep promoter-CAT constructs, expression was inhibited. Inhibition decreased with elevation of plasmid concentration and was increased with an increase in nuclear extract concentration. Since specific DNA-protein interactions were diminished by the combination of oocyte and Drosophila nuclear extracts in gel retardation assays, a sequestering-type mechanism of repression has been proposed.

Previous characterisation of the Drosophila ras2/rop bidirectional promoter regulatory mechanism revealed two DNA-binding protein factors. These were named DCF (Drosophila CACCC-binding Factor) and DREF (Drosophila Replication Related Element-binding Factor) respectively. A major protein complex consisting of these two transcription factors specifically binds the CACCC and DRE sites. In the present study we show that limited trypsin digestion of the major complex dissociates DCF and DREF, in the active conformation, able to bind the CACCC and DRE motifs. In addition, we show that DNA-binding activity of the DREF/DCF heterodimer is specifically inhibited by the presence of purine nucleotides, while that of the individual factors remains unaltered.

Alpha ecdysone is naturally present in the leaves of some plants, including the carcinogenic plant bracken fern (Pteris aquilina). Feeding mice with alpha-ecdysone at a dose level of 3 ppm/25 g body weight, 2 times per week for 22 months induced a significant increase in the body weight of the animals. Breast and lung tumors developed in the experimental mice. Other pathological changes such as fibrocystic disease of the breast and bronchocentric granulomas appeared in these animals. The results of this study proved that alpha-ecdysone may be one of the active carcinogens in bracken fern plant which was responsible for induction of tumors in different animals investigated by previous authors.