AN ABSTRACT OF THE THESIS OF Su-Jun Lee for the degree of Doctor of Philosophy in Toxicology presented on

Abstract approved: Rainbow trout (Oncorhynchus mykiss) has been used as a model species for toxicology and cancer study due to its sensitivity to chemicals. Previous purified trout LMC5 P450 showed 6P-hydroxylation activity of steroids and cross-reacted with antibodies raised against human CYP3A4 on the SDS-PAGE. These findings suggest that rainbow trout P450 systems include CYP3A forms. Therefore, study was conducted to isolate and to characterize the CYP3A forms in rainbow trout. A new CYP3A form containing 518 amino acids was cloned and assigned to CYP3A27 by the Cytochrome P450 Nomenclature Committee to represent the first CYP3A subfamily member characterized in aquatic species. The major expression site for CYP3A27 mRNA was intestinal ceca and liver. Southern blot analysis demonstrated that multiple CYP3A27-related genes exist in rainbow trout. To examine the cellular localization and the expression pattern of CYP3A27, immunohistochemical (IH) studies were performed. The relative distribution of CYP3A27 mRNA and protein along the trout gastrointestinal trac