Transcription of Djun from D. melanogaster Is Positively Regulated by DTF-1, AP-1, and CREB Binding Sites

Abstract

Djun is the homolog of the mammalian proto-oncogene jun in D. melanogaster, where it encodes a component of an AP-1-like nuclear DNA binding protein, or transcription factor. Djun, unlike its vertebrate counterparts, contains an intron in its 5′ noncoding region. The expression of Djun in cultured Schneider line 2 cells is controlled by multiple cis-acting elements in its promoter region and the 5′ noncoding region of the transcription unit. A 43-bp 5′ upstream promoter region is necessary for the transcription activity of Djun. Deletion of this fragment decreased transcriptional activity by 67-fold. This region includes a TATA box and a sequence similar to the Drosophila transcription factor 1 (DTF-1) consensus sequence (GCAACA T/C G/C). A large DNase I footprint covering both the DTF-1 binding site and the TATA box was detected in this region when incubated with nuclear extract from Drosophila embryos, suggesting interactions with related transcription factors. This 43-bp sequence alone, containing the DTF-1 binding site and TATA box, however, is not sufficient for transcription activity. An 80-bp sequence including the start of transcription has considerable basal activity. An intragenic region containing an AP-1 site and a CRE site modulates or fine tunes activity of the promoter. Its activity as an enhancer is reduced when moved upstream in either orientation. An extragenic region containing two AP-1 sites similarly affects promoter activity.