Four independent clones containing a part of the P-450 (SCC), cholesterol desmolase, gene were isolated from human genomic libraries using bovine P-450 (SCC) cDNA as a probe. These clones covered the entire P-450 (SCC) gene except for a part of the 1 st intron. The gene is at least 20 kb long and is split into 9 exons by 8 introns. The sequence analysis revealed that the nine separated exons code for a primary structure consisting of 521 amino acids which shows 72%. homology with that of bovine P-450 (SCC). A CATT sequence and a TATAAT sequence, which are possibly a “CAT” box, and a “TATA” box, respectively, are present 129 and 91 by upstream from the initiation codon. An unusual exon/intron functional sequence that begins with GC was found in the 6th intron of the gene. A putative extension peptide consisting of 39 amino acids was found in the sequence of human P-450 (SCC) by comparison with that of the bovine counterpart. Two conserved regions were found in the extension peptide of these two forms of P-450 (SCC), suggesting a functional role of the portions in the mitochondrial localization and processing of P-450 (SCC) precursor. The mature form of human P-450 (SCC) has only one cysteine residue, which was located in the center of the HR2 region (Gotoh et al. (1983) J. Biochem. 97, 807-817). This observation established beyond doubt that the sole cysteine residue in the HR2 region is the 5 th ligand to the heme.
The Japanese Biochemical Society