The 5'-region of the P450XIA1 (P450scc) gene contains a basal promoter and an adrenal-specific activating domain.

The first step to the synthesis of all steroids is catalyzed by P450scc. We constructed nine deletion mutants of the 5'-region of the P450scc gene and connected them to a CAT reporter gene to assay transcriptional activity of the P450scc promoter. A short 145 bp fragment stimulated transcription by two fold. This DNA was active in all cells tested irrespective of their tissue origin and steroidogenic activity. DNA at -145/-573 of the upstream region did not increase transcription any further. DNA including 2500 bp of the upstream region stimulated transcription by 10 fold only in adrenal Y-1 cells. Hence in the -145 region contains a low level P450scc promoter and the 2500 bp DNA possesses an adrenal specific enhancing element.