The objective of the proposal is to determine the molecular events involved in replication of a chemical carcinogen damaged DNA template in cultured mammalian cells treated with the proposed ultimate carcinogenic form of benzo(a)pyrene, 7,8 dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, (B(a)P-diol-epoxide). The proposed studies make use of primary cultures of mouse epidermal cells and Vero cells (an African green monkey kidney cell line). Four specific objectives include 1) to continue to develop evidence for "gapped DNA synthesis" in epidermal cells using DNA fiber antoradiography in order to study DNA fork progression and replicon function, 2) to determine if B(a)P-diol-epoxide DNA adducts in Vero cells act as absolute blocks to DNA replication and if not to determine the mechanism by which the whole genome is replicated, 3) to determine if B(a)P-diol-epoxide treatment of epidermal cells or Vero cells results in host cell reactivation of either UV-irradiated or B(a)P-diol-epoxide treated herpes simplex virus and whether reactivation is mutagenic to the virus and inducible, 4) to determine at the molecular level whether there is an enhanced rate of DNA elongation which might be related to B(a)P-diol-epoxide induced reactivation of the herpes simplex virus.