Chicken bone marrow cells transformed by reticuloendotheliosis virus (REV) produce in the cytoplasm a ribonucleoprotein (RNP) complex which has a sedimentation value of approximately 80 to lOOS and a density of 1.23 g/cm3. This RNP complex is not derived from the mature virion. An endogenous RNAdirected DNA polymerase activity is associated with the RNP complex. The enzyme activity was completely neutralized by anti-REV DNA polymerase antibody but not by anti-avian myeloblastosis virus DNA

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... erase antibody. The DNA product from the endogenous RNA-directed DNA polymerase reaction of the RNP complex hybridized to REV RNA but not to avian leukosis virus RNA. The RNA extracted from the RNP hybridized only to REV-specific complementary DNA synthesized from an endogenous DNA polymerase reaction of purified REV. The size of the RNA in the RNP is 30 to 35S, which represents the subunit size of the genomic RNA. No 60S mature genomic RNA was found within the RNP complex. The significance of finding the endogenous DNA polymerase activity in the viral RNP in infected cells and the maturation process of 60S virion RNA of REV are discussed. which has properties markedly different from, and which appears to be the precursor of, the mature virion. This report describes the characterization of this complex with regard to its physical properties, the size and specificity of its genetic content, and its associated DNA polymerase activity. MATERIALS AND METHODS Cells and viruses. REV-T-transformed chicken BMC were a kind gift from H. Bose, University of 34 on May 4, 2020 by guest http://jvi.asm.org/ Downloaded from on May 4, 2020 by guest http://jvi.asm.org/ Downloaded from on May 4, 2020 by guest