Infectious murine leukemia virus from DNA of virus-negative AKR mouse embryo cells

DNA from virus-negative AKR mouse embryo cells is infectious for NIH 3T3 cells if the transfected cells are treated with 5-iododeoxyuridine (IdUrd) either before or after addition of the DNA. The virus isolated after transfection of the AKR DNA is an ecotropic murine leukemia virus (MuLV) indistinguishable from endogenous AKR MuLV. The AKR DNA is not infectious in the absence of IdUrd treatment of the recipient cells. DNA from AKR cells treated with IdUrd before DNA isolation is not infectious unless the recipient cells have been treated with IdUrd. Transfected DNA from NIH mouse cells is not infectious even when the recipient cells have been treated with IdUrd. DNA from cells chronically infected with AKR MuLV or Rauscher MuLV is infectious with or without IdUrd treatment of the recipient cells, but the infectivity is not enhanced by IdUrd. The results indicate that the endogenous AKR MuLV DNA genome is potentially infectious. The data are consistent with an IdUrd-sensitive restriction in the recipient NIH 3T3 cells that prevents viral replication from endogenous AKR MuLV DNA but does not prevent viral replication from MuLV DNA of productively infected cells.