Structure of the rat gene encoding the mitochondrial benzodiazepine receptor

The gene encoding the rat mitochondrial benzodiazepine receptor (MBR) was cloned and characterized. Hybridization of a previously cloned cDNA for MBR to genomic Southern blots indicated that the gene was probably present at one copy per haploid genome. Rapid amplification of cDNA ends with rat adrenal RNA was used to obtain 47 nt of additional sequence upstream from our previously cloned MBR cDNA proving to be a crucial step in cloning the first exon of this gene. The MBR gene is comprised of four exons spanning approx. 10 kb. The first intron, contained within a 8-kb stretch of this gene, is located within the 5'-untranslated sequence, whereas the remaining two introns are much shorter (641 and 854 bp) and interrupt the coding sequence. The third intron contains sequences homologous to rodent B1 repetitive elements and a novel sequence closely resembling part of a repetitive element belonging to the Alu family in humans. The transcription start point was mapped by S1 nuclease protection assays suggesting that the first exon is just 56 bp in length. The sequence upstream from this region contains three GC boxes but lacks other known consensus recognition sites for sequence-specific transcription factors.