Genetic polymorphisms for a phenobarbital-inducible cytochrome P-450 map to the Coh locus in mice.

Southern blot analysis suggests that multiple sequences homologous to a phenobarbital-inducible cytochrome P-450 cDNA are present in the rat and mouse genomes. A cDNA (pP-450b-5) to a major phenobarbital-inducible cytochrome P-450 mRNA species in the rat detected 6 polymorphic DNA fragments when hybridized to DNA from C57BL/6J and DBA/2J mice restricted with endonucleases EcoRI, BamHI, and PvuII. Using the BXD recombinant inbred strains, five of these polymorphisms were mapped to the Coh (coumarin hydroxylase) locus on chromosome 7 of the mouse. The Coh locus has previously been shown to code for a phenobarbital-inducible enzyme, believed to be a cytochrome P-450, which catalyzes the conversion of coumarin to 7-hydroxycoumarin (umbelliferone). The DNA polymorphisms appear to reflect changes in either cytochrome P-450 genes or pseudogenes that are very closely linked to the gene responsible for differential coumarin hydroxylase in mice or it may represent a change(s) in the Coh gene itself. The region of the Coh locus on chromosome 7 may be the site of a cluster of cytochrome P-450 genes.