Identification of a sequence motif upstream of the Drosophila dopa decarboxylase gene that enhances heterologous gene expression.

In this paper we have examined the role that element S, a DNA sequence motif found approximately 215 bp upstream of the Dopa decarboxylase (Ddc) gene, might play in regulating Ddc expression. Nearly identical versions of the element are present upstream of four other Drosophila genes. For two of these, the element appears to be an important component of the upstream regulatory region, since mutations in it reduce expression of the downstream gene. Because an element S polymorphism differentiates the Ddc+ allele of an inbred laboratory strain from the Ddc+4 allele present in a strain isolated from the wild, we decided to test the activity of both forms. Oligonucleotides containing Ddc+ or Ddc+4 versions of element S were synthesized and their ability to drive the expression of an heterologous (Adh) reporter gene at the second molt was examined. Transgenic larvae carrying the element S-Adh fusion constructs consistently exhibited Adh levels that were elevated 1.5-fold above those seen in control organisms. We have also determined the effects of element S in white prepupae and once again, ADH expression levels were significantly above controls in both groups of transformants carrying the element S construct. The results point to a functional role for element S. Since reporter gene expression in third instar larvae was restricted to tissues where ADH is normally found, we conclude that element S is not involved in directing the tissue specificity of Ddc expression.(ABSTRACT TRUNCATED AT 250 WORDS)