Functional analysis of NTF-1, a developmentally regulated Drosophila transcription factor that binds neuronal cis elements

Abstract

In an effort to characterize sequence-specific transcription factors that regulate gene expression during Drosophila development, we identified and purified a novel DNA-binding activity (NTF-1). The purified protein consists of several polypeptides that bind selectively to a functionally important cis-control element of the Ultrabithorax (Ubx) promoter and to the neurogenic elements of both the dopa decarboxylase (Ddc) and fushi tarazu (ftz) promoter/enhancer regions. Purified NTF-1 activates transcription in vitro in a binding site-dependent manner through upstream sequences of the Ubx promoter. A cDNA clone encoding the open reading frame of NTF-1 was isolated, and the deduced primary amino acid sequence of NTF-1 includes a glutamine-rich region reminiscent of the transcriptional activation domains found in Sp1 but no recognizable DNA-binding domain. NTF-1 expression is temporally regulated during embryonic development. In addition, in situ hybridization experiments revealed that NTF-1 is transcribed in a spatially restricted pattern in the embryo, with the highest level of expression observed in the epidermis and a subset of cells in the CNS. Expression of the NTF-1 cDNA in mammalian cells yields a protein that displays DNA-binding and transcriptional activities indistinguishable from that of the collection of proteins isolated from Drosophila embryos. These findings suggest that NTF-1 is a member of a family of developmentally regulated transcription factors that may be involved in directing the expression of genes such as Ubx, Ddc, and ftz in neuronal cells.