We have used DNA transfection to study the endogenous retrovirus genomes inherited by uninfected mouse cells. Quantitative assays for infectious DNAs of ecotropic and xenotropic murine leukemia viruses (MuLVs) were developed using donor DNAs of cells that were exogenously infected with ecotropic Moloney, AKR or BALB MuLVs, or with xenotropic AKR, BALB or NZB MuLVs. The DNAs of cells exogenously infected with ecotropic MuLVs had specific infectivities of approximately 0.5 infectious units (IU) per μg DNA in transfection assays on NIH/3T3 cells. The DNAs of cells exogenously infected with xenotropic MuLVs had specific infectivities of approximately 0.2 IU/μg DNA in transfection assays on mink CCL64 cells. In contrast, the DNAs of uninfected NIH/3T3, BALB/3T3 and AKR-2B mouse cells were noninfectious when assayed for infectious endogenous ecotropic MuLV DNAs (<0.001 IU/μg DNA). Similarly, the infectivities of xenotropic MuLV DNAs of uninfected NIH/3T3, BALB/3T3, AKR-2B and NZB-Q mouse cells were more than 100 fold lower than the infectivities of DNAs of xenotropic MuLV-infected cells. Furthermore, the DNAs of BALB/3T3 cells transformed by Kirsten murine sarcoma virus (MSV) or by simian virus 40 (SV40) were noninfectious for either ecotropic or xenotropic MuLV, although these cells contained infectious transforming DNAs of MSV or SV40. The endogenous MuLV genomes of uninfected mouse cells thus appeared to differ from the MuLV proviruses of MuLV-infected cells. These results are consistent with the hypothesis that endogenous MuLV genomes are linked to cellular DNA sequences which result in both inefficient transcription of endogenous MuLV genomes and the reduced infectivity of endogenous MuLV DNAs in transfection assays.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)