This research team is interested in the Ah locus. This gene encodes a cytosolic receptor protein, which controls the levels of a particular subset of drug-metabolizing enzymes. This genetic system is clearly present and similar in all mammals, including human. In the mouse, three drug-metabolizing enzymes (monooxygenases) regulated by the Ah receptor have been named cytochrome P1-450, P2-450 and P3-450 and, by definition, metabolize most efficiently benzo[a]pyrene, isosafrole and acetanilide, respectively. These three membrane-bound proteins have been highly purified, and antibodies have been developed that most specifically inhibit benzo[a]pyrene, isosafrole and acetanilide metabolism, respectively. Full-length cDNA clones have been identified, and genomic clones for P1-450 and P3-450 have been isolated and partially characterized. Nucleotide sequence analysis is near completion for the mouse cDNA and genomic clones. Several phenobarbital-inducible proteins--PPhi-450, PBeta-450 and PTau-450--have been partially purified, and an antibody developed against PTau-450 most specifically blocks coumarin 7-hydroxylase activity, which has been defined as the murine Coh locus. A cDNA clone for a phenobarbital-inducible gene has been isolated and partially sequenced; since this gene is not under Ah receptor control, this gene will serve as a valuable control for various comparative experiments with the Ah locus-associated regulatory mechanism(s). Data about P-450 genes regulated by the Ah receptor and one or more P-450 genes not under Ah receptor control should provide valuable insight into the total number of P-450 proteins that an organism is capable of expressing, the total number of subsets (or P-450 gene families within the entire P-450 superfamily), the mechanism of P-450 induction, and the evolutionary significance of this gene superfamily. Using a mouse P1-450 cDNA clone, we have also isolated human genomic clones corresponding to mouse P1-450 and P3-450, and further characterization of these is underway.