In vitro transmission of mouse leukemia virus to restrictive mouse cells: necessity for mixed infection by two different leukemia viruses]

The plaque formation of murine leukemia virus (MuLV) in non permissive mouse cells (N-tropic MuLV in B-type cells, or B-tropic MuLV in N-type cells) was increased by murine sarcoma virus whose plaque-forming activity was extremely low (MuSV XC-). The infection of N-tropic MuLV in B-type cells was increased by MuSV XC- propagated only in N-type cells but not in B-type cells, and the infection of B-tropic MuLV in N-type cells by MuSV XC- propagated only in B-type cells but not in N-type cells.