Characterization of reticuloendotheliosis virus strain T DNA and isolation of a novel variant of reticuloendotheliosis virus strain T by molecular cloning

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Abstract
Reticuloendotheliosis virus strain T (REV-T) is a highly oncogenic avian retrovirus which causes a rapid neoplastic disease of the lymphoreticular system. Upon infection, this virus gives rise to 2 spp. of unintegrated linear viral DNA which are 8.3 and 5.5 kilobase pairs (kbp) long and represent the helper virus (REV-A) and the oncogenic component (REV-T), respectively. Restriction endonuclease cleavage maps of these 2 DNA components indicate that REV-T DNA has a large portion of the genome deleted with respect to REV-A DNA and a substitution .apprx. 0.8-1.5 kbp long that is unrelated to REV-A DNA. These additional sequences comprise the putative transforming region of REV-T (rel). A chicken spleen cell line transformed by REV-T produced virus which upon infection gives rise to 3 spp. of unintegrated linear viral DNA (8.3, 5.5 and 3.3 kbp). The proviruses of the 8.3- and 3.3-kbp species from this cell line were isolated by cloning in the phage vector Charon 4A. Restriction enzyme mapping showed that the 2 proviral clones are proviruses of REV-A and a variant of REV-T, respectively. A subclone of the variant REV-T provirus specific for the rel sequences of REV-T was used as a hybridization probe to demonstrate that the rel sequences are different from the putative transforming sequences of Schmidt-Ruppin Rous sarcoma virus strain A, avian myelocytomatosis virus, avian myeloblastosis virus, avian erythroblastosis virus, Abelson murine leukemia virus and Friend erythroleukemia virus. The rel-specific hybridization probe was used to identify a specific set of sequences which are present in uninfected avian DNA digested with several restriction enzymes. The corresponding cell sequences are not arranged like rel in REV-T.