The Drosophila Fos-related AP-1 protein is a developmentally regulated transcription factor

Drosophila AP-1 consists of two proteins (dFRA and dJRA) that have functional and structural properties in common with mammalian Fos and Jun proto-oncogene products. Here, we report the isolation and characterization of cDNAs encoding the full-length dFRA and dJRA proteins. The predicted amino acid sequences reveal that both proteins contain a bipartite DNA-binding domain consisting of a leucine repeat and an adjacent basic region, which are characteristic of members of the AP-1 family. By using protein translated in vitro or expressed in Escherichia coli, we demonstrate that dFRA, in contrast to the mammalian cFos proteins, recognizes the AP-1 site on its own and activates transcription in vitro in the absence of dJRA or Jun. Heteromeric complexes formed between dFRA and dJRA bind the AP-1 site better than either protein alone, and the two proteins activate transcription synergistically in vitro. In the developing embryo, dFRA mRNA is first expressed in a limited set of cells in the head and is later restricted to a subset of peripheral neurons, several epidermal cells near the muscle attachment sites, and a portion of the gut. In contrast, dJRA appears to be uniformly expressed at a low level in all cell types. These results indicate that dFRA is a developmentally regulated transcription factor and suggest that its potential interplay with dJRA plays an important role in cell-type-specific transcription during Drosophila embryonic development.