MULTIPLE REGIONS OF A DIVERGENT PROMOTER CONTROL THE EXPRESSION OF THE AGROBACTERIUM-RHIZOGENES AUX1 AND AUX2 PLANT ONCOGENES

The two auxin biosynthesis genes, aux1 and aux2 of Agrobacterium rhizo genes strain A4, are located on opposite DNA strands with a short inte genic region (394 bp) between their coding sequences. A functional ana lysis of this divergent promoter is presented. The transcription initi ation sites of the two aux genes were determined and regions important for promoter activity were identified by deletion and transient expre ssion analyses in tobacco protoplasts. The promoter activity of the au x intergenic region was demonstrated. A strong enhancer element contai ned within an 84 bp promoter fragment was identified. Far upstream reg ions were shown to have negative effects on the promoter activity of t he short intergenic region. Interactions between positive elements in the intergenic region and negative effects of the upstream sequences m ay be the basis of strict control of the auxin biosynthesis necessary for the induction and maintenance of hairy root growth.