Quantitation of enzyme reactions which determine the extent and selectivity of DNA modification by benzo(a)pyrene will be pursued in both rat hepatocytes, lung cells, and in mouse fibroblast lines. Activation by mixed-function oxidation and epoxide hydratase will be related to enzymatic protection by UDP-glucuronyl transferases, sulfotransferases, and glutathione-S-transferases. DNA modification during benzo(a)pyrene metabolism will be analyzed in intact cells and in subcellular incubations consisting of DNA (or nuclei) and fractions (or purified enzymes) from the cells at approximate cellular levels. Selectivity and extent of DNA-modification will be analyzed using high pressure liquid chromatography of nucleoside-hydrocarbon conjugates and by use of selective S1-endonuclease and DNase I digestion techniques. DNA modification and excision repair will be correlated with cell transformation using C3H/10 T1/2 (transformable) and C3H/CVP (non-transformable mouse fibroblast lines, polycyclic hydrocarbon metabolites of differing transforming capability, and cell-cycle manipulation which change transformation frequency.