This research proposal is concerned with the investigation of the proviral DNA of reticuloendotheliosis virus (REV). The REVs are newly described avian RNA tumor virus which are etiologic agents for reticuloendotheliosis in chicken and ducks and leukemia in turkeys. REV is a prototype virus to study the virus induced tumors because REV is highly virulent; its incubation period is short; mortality approaches 100%; it has a wide host range; and it is easy to grow with high titer. Our specific aims directed toward 1) isolation and characterization of REV specific provirus DNA both pre and post integration into the chromosoma1 DNA, 2) study the REV specific DNA provirus integration site(s), 3) synthesis of in vitro the transfectable DNA provirus using mature virions and viral precursor ribonucleoprotein complex. The results of these experiments will elucidate 1) the size and conformation of infectious DNA which will implicate the genetic complexity of REV and 2) the location of proviral DNA integration site and its relationship to the phenotypic expression of REV-transformed cells. During the course of our investigation, we have directed ourselves toward 1) in vitro synthesis of full length proviral DNA from the endogenous DNA polymerase reactions using the intracellular ribonucleoprotein complex and purified virions of REV in order to study the necessity of 60S RNA for the virus replication. We have also studied the provirus integration site in the REV-infected chicken cell chromosomes by the nucleic acid hybridization and DNA transfection experiments. In the forthcoming grant periods, we will direct our research toward 1) the investigation of provirus integration site(s) using various restriction endonuclease to cut the REV transformed cellular DNA and anneal the fragments of DNA with radioactive phosphate labeled viral RNA using the Southern blot technique; 2) investigation of endogenous REV sequences in mammalian species since we and others have some evidences which suggest that REV may have been evolved from a mammalian host rather than avian origin.