BSF1, a novel brain-specific DNA-binding protein recognizing a tandemly repeated purine DNA element in the GABAA receptor delta subunit gene.

The rat GABAA receptor delta subunit gene has been isolated and its promoter mapped to facilitate studies of neuron-specific gene transcription. The gene is transcribed from a single promoter with several clustered transcriptional initiation sites. The major start site maps to a prototype initiator sequence located in the center of a TATA-less CpG-rich island. Analysis of the 5'-flanking region of the GABAA receptor delta subunit gene revealed a novel tandemly repeated purine sequence element. Furthermore, gel retardation assays identified several tissue-specific and ubiquitous proteins that bind to this sequence. One of these factors, brain-specific factor (BSF) 1, was only observed in extracts from brain and was distinct from BETA and PAL, two DNA-binding proteins with similar purine-rich recognition sequences. The distribution of BSF1 in brain closely matched the expression pattern previously determined for the delta subunit mRNA, and its binding activity appeared simultaneously with GABAA receptor delta subunit mRNA during differentiation of cerebellar granule cells in vitro. Our data therefore suggest that BSF1 is a novel brain-specific and neuronal cell type-enriched factor possibly involved in differential transcription of the GABAA receptor delta subunit gene.