1. Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, Portland, Oregon 97239, Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas 77555, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, and Department of Chemistry, Center in Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235