The proposed research is a continuation of the program already under way and aims to dissect, understand and influence the function and intracellular relationships of the cell's second genetic system, the mitochondria, in oncogenic virus induced malignancy. We have found distinct qualitative and quantitative differences in the mitochondrial DNA replication apparatus, directly correlated with the phenotypic expression of oncogenic virus transformation. The following parameters will be analyzed using normal as compared to oncogenic virus-transformed animal cells ( including an ideally controlled cell system of chick embryo fibroblasts (CEF) infected by wild-type and temperature-sensitive mutants of Rous sarcoma viruses (RSV): (1) Structural characteristics of the isolated initiation sequence of mtDNA replication; (2) Structural and functional properties of the isolated mtDNA-membrane complex; (3) Further purification and properties of mitochondrial DNA polymerase (template specificity. fidelity of copying, response to inhibitors; (4) Further analysis of mitochondrial and nuclear DNA methylases with respect to molecular weights, specificity and response to inhibitors; (5) Analysis of unintegrated proviral DNA and other newly found DNA species by electron microscopy, restriction endonucleases and hybridization in early infected CEF.