Abstract
FMR antigens are found on the surface of cells infected with Friend, Moloney, and Rauscher murine leukemia viruses (MuLV). These antigens are serologically distinct from the G cell surface antigens that are found on cells infected with endogenous MuLV (AKR and Gross virus). Cell surface antigens of both virus groups are immunogenic in mice, and immunization with appropriate virus-infected cells leads to the production of cytotoxic antisera. The cytotoxic activity of FMR antisera can be absorbed by disrupted preparations of Rauscher MuLV, but not by AKR MuLV. FMR antisera precipitate the viral envelope proteins gp70, pl5(E), and p12(E) from detergent-disrupted preparations of [3H]leucine-labeled MuLV. The reaction of these antisera with p15(E) and p12(E) proteins is directed against group-specific antigens and can be absorbed with AKR MuLV; in contrast, the reaction of these antisera with gp70 is directed against type-specific antigens and is absorbed only by viruses of the FMR group. In immune precipitation assays with detergent-disrupted 125I surface-labeled cells, FMR antisera react only with type-specific antigens of the viral envelpe protein. On the basis of these findings we conclude that the FMR cell surface antigen is a determinant on the MuLV env gene product.