Lightfoot, K., Department of Zoology, University of the Witwatersrand, WITS, 2050 Johannesburg, South Africa
Duarte, R., Department of Zoology, University of the Witwatersrand, WITS, 2050 Johannesburg, South Africa
Segev, O., Department of Zoology, University of the Witwatersrand, WITS, 2050 Johannesburg, South Africa

The Drosophila ras2 promoter is an authentic bidirectional promoter governing the expression of both the Dras2 and rop genes by a single mechanism. Characterisation of the Dras2/rop promoter has revealed that a unitary complex (M) interacts with two promoter sub-domains (regions A and B). Two distinct transcription factors (factors A and B), which make up the major complex (M), bind regions A and B, respectively. We have analyzed the putative CACCC element and AP-1-like sequence contained within region B (-41 to -20) of the Dras2/rop promoter. It was found that AP-1 is not involved in Dras2 expression as is the case for the human Ka-ras1 gene. The entire CACCC motif (-34 to -21) shares 83% homology with the conserved mammalian element. Detailed mutational analysis has however revealed that the CACCC core sequence (-27 to -23) is vital for Dras2/rop recognition by factor B. The cytosine residues at positions -27, -25, -24 and -23 were observed to play a critical role in factor B recognition. Factor B has been purified as a 43 kD polypeptide as measured by SDS-PAGE and the relative mass was confirmed by photo-chemical crosslinking. Our findings are the first report of the conservation of the mammalian CACCC motif in Drosophila.