STEROL 14-DEMETHYLASE P450 (P45014DM-ASTERISK) IS ONE OF THE MOST ANCIENT AND CONSERVED P450 SPECIES

To determine the orthology of sterol 14-demethylase (P45014DM), the on ly known P450 enzyme distributed widely in eukaryotes with a conserved metabolic role, the full-length amino acid sequences of rat and human P45014DMs were determined from the cloned cDNA sequences, and compare d with those of the corresponding fungal proteins (CYP51), The amino a cid identity value between given pairs of P45014DMs ranged from 93% (h uman/rat) to 39% (human or rat/Saccharomyces cerevisiae), All the P450 14DMs formed a single cluster in a phylogenetic tree constructed from representative P450 protein sequences currently available, The nearest neighbors to the P45014DM cluster in the phylogenetic tree were CYP7 (cholesterol 7 alpha-hydroxylase) and CYP8 (prostacyclin synthase), an d the divergence point of fungal and mammalian P45014DMs was clearly m ore recent than that of P45014DM and CYP7/CYP8, These lines of evidenc e show that fungal and mammalian P45014DMs are really orthologous. Thi s is the first example of orthologous P450s occurring in distinct king doms, P45014DM may be an ancient P450 which arose before the divergenc e of major eukaryotic branches and has been conserved throughout evolu tion, The amino acid identity value (93%) between human and rat P45014 DMs was comparable to those observed for some housekeeping enzymes, In addition, a processed pseudogene of P45014DM was found in a rat genom ic DNA library, suggesting the expression of P45014DM in germ line cel ls, These facts suggest that P45014DM may be a housekeeping enzyme ess ential for the viability of mammals.