Tal, A., Department of Zoology, University of Witwatersrand, Private Bag 3, Witwatersrand 2050, South Africa
Veale, R., Department of Zoology, University of Witwatersrand, Private Bag 3, Witwatersrand 2050, South Africa
Segev, O., Department of Zoology, University of Witwatersrand, Private Bag 3, Witwatersrand 2050, South Africa

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.