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-Iike 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 Ha-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.

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