In recent studies that addressed the transcriptional control of steroid synthesis, a transcriptional regulating protein of 132 kDa (TReP-132) was cloned and demonstrated to regulate expression of the human P450 side chain cleavage (P450scc) gene. In the present study, we describe the cloning and characterization of the mouse orthologue of the human factor, mouse transcriptional regulating protein (mTReP-132). mTReP-132 encodes a 1216-residue protein that is 85.5% homologous to the human protein. Both factors contain characteristic motifs, namely glutamine-, proline- and acidic-rich regions. The primary structure also exhibits two zinc fingers of the C(2)H(2) subtype, suggesting that this protein has the ability to act as a DNA binding transcription factor. mTReP-132 may also be a co-regulator of nuclear receptors because of two nuclear box motifs in this protein. Northern blot analysis demonstrated the expression of two transcripts of 4.4 and 7.5 kb in several tissues, but expression was clearly highest in the brain, thymus and testis of mice. In the brain, the hybridization signal was quite localized and strong in the basal ganglia, hippocampus, piriform cortex, cerebral cortex, ventromedial nucleus of the hypothalamus, and the dorsal and superior central nuclei of the raphe. Although classical steroidogenesis pathways have yet to be firmly established in the brain, expression of both mTReP-132 and P450scc provides anatomical evidence that mTReP-132 may regulate this key steroidogenic enzyme within specific regions involved in behavioral and psychiatric disorders. Moreover, the presence of both mTReP-132 and steroidogenic factor 1 (SF-1) transcripts in the ventromedial nucleus of the hypothalamus suggests a role for mTReP-132 in brain development and function. The molecular cloning and the highly specific expression of mTReP-132 across the brain further consolidate the hypothesis that this tissue is able to synthesize de novo steroids in a region-specific manner.