Characterization of the fbr‐murine osteosarcoma virus complex: FBR‐MuSV encodes a fos‐derived oncogene

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Abstract
The FBR murine osteosarcoma virus complex, isolated from a radiation‐induced osteosarcoma of an X/Gf mouse causes the rapid appearance of osteosarcomas in newborn mice and transforms fibroblasts in vitro. The two components of the FBR‐viral complex have been isolated separately in tissue culture: FBR‐MuLV by end‐point dilution and FBR‐MuSV by the establishment of mouse [FBR‐NP117 (NIH 3T3)] and rat non‐producer cell lines [FBR‐NP415 (REF)]. The host range and RNase TI fingerprint analysis of FBR‐MuLV demonstrated a pattern closely related to, but distinguishable from, Akv‐MuLV. Transformed cells from both mice and rats contain a rescuable FBR‐MuSV genome. These pseudotypes produce foci in tissue culture and induce osteosarcomas in susceptible mouse strains. An FBR‐MuSV (FBR‐MuLV) cDNA probe detects a 5.2 kb Hindlll and a 9.5 kb EcoRI FBR‐MuSV‐specific fragment in FBR‐MuSV‐transformed non‐producer rat cells. The same fragments hybridized with a fos specific probe, demonstrating that FBR‐provirus contains a c‐fos‐derived onc‐gene.