Fine-structure mutational analysis of a stage- and tissue-specific promoter element of the Drosophila glue gene Sgs-3.

The Sgs-3 gene of Drosophila melanogaster exhibits a tightly regulated pattern of expression governed by two functionally equivalent elements within 1 kb of the gene, each of which is sufficient to confer third-instar salivary gland-specific transcription. In this report we describe a detailed functional analysis of one of these, the proximal element. To determine the nucleotides responsible for specific expression, we have introduced mutations into the proximal element and then assessed the effects of each alteration on expression in the developing animal. We have identified six particularly important base pairs which are located in two regions separated by nonessential sequences. These base pairs, along with some surrounding sequence, are conserved within the upstream regions of the three glue genes at 68C. Nearly identical groups of base pairs can be found upstream of the other glue genes which have been cloned. This analysis has allowed us to derive a consensus sequence, which we believe contains binding sites for two different factors which interact to direct third-instar salivary gland-specific expression.