The genomes of equine herpesvirus (EHV) type 1,2(a cytomegalovirus), and 3(veneral disease virus) will be mapped by restriction enzyme methods, and DNA sequences shared among the three viral DNAs will be identified by blot hybridization analyses. In addition the genomic structure of EH-V-1 defective interfering particles, shown to mediate the co-establishment of persistent infection and oncogenic transformation, will be elucidated. Restriction enzyme fragments encompassing the entire genomes of the three viruses will be cloned as recombinant molecules (plasmids) in E. coli hosts to provide quantities of DNA fragments sufficient to be used as probes in biochemical studies of herpesvirus oncogenesis. EHV- 1, 2, & 3 transformed cells (mouse and hamster), tumor tissues, and tumor cell lines developed in our laboratory will be analyzed for integrated viral DNA sequences by Cot and blot hybridization techniques. In addition, conjoint sequences (cell DNA fragments containing integrated viral DNA sequences) will be cloned in E. coli hosts via packaging into lambda phage particles as vectors, and these DNA molecules will be assayed by restriction enzyme digestion followed by blot hybridization with radiolabeled cloned probes to discern the identity, nature, and arrangement of viral genes integrated into cellular DNA during herpesviral oncogenic transformation and tumorigenesis. Emphasis will be given to experiments designed to determine whether a specific viral gene or genes are involved in oncogenesis and whether this gene or genes are virus type-unique or are type-shared. Lastly, persistently-infected cells established by infection with live EHV-1 enriched for defective interfering particles will be analyzed to determine the nature and arrangement of viral genomes maintained within these cells.