We describe novel photochemical and enzymatic methods for mapping drug and carcinogen binding sites on DNA. We propose to use those methods to develop rules for predicting benzo(a)pyrene-diol-epoxide (BPDE) binding sites on eukaryotic genes. As a class, we propose to use the photochemical methods as tools to explore the relation between DNA sequence and DNA structure in the chicken Beta A globin gene, and in the SV40 enhancer/origin of replication. In a separate set of BPDE binding experiments we will determine if the c-myc oncogene contains high affinity carcinogen binding sites and will map the distribution of BPDE molecules within such regions at one base resolution. We also describe methods for mapping BPDE binding to oncogenes in intact nuclei. The goal of these experiments is to determine if, in a mouse B cell, the c-myc gene is involved in chemical carcinogenesis because the gene is sensitive to attack by an environmental toxin. We also propose to map BPDE binding sites on the myc gene in BALB/c-3T3 cells. The goal of those experiments is to determine if carcinogen binding to an oncogene shows cell specific differences.