Synthesis of Murine Leukemia Virus Proteins Differentiating Friend Erythroleukemia Cells

In agreement with previous observations, the Friend 745 line of virus-induced erythroleukemia cells can be induced by dimethyl sulfoxide to synthesize hemoglobin and to increase simultaneously their content of morphologically recognizable virus particles, especially in cytoplasmic vesicles. In apparent contrast to the electron microscopic results, the cellular content of the major murine leukemia virus (MuLV) proteins p30 (the major internal core protein) and gp70 (the envelope glycoprotein) were measured by radioimmunoassay and were found to be approximately the same in control and in induced cells. Control and induced cells are also approximately as active in the synthesis of the protein precursors of p30, reverse transcriptase, and gp70 in the processing of these precursors by proteolysis and glycosylation. Furthermore, the noninfectious MuLV synthesized by this cell line is released into the culture medium to the same extent by control and induced cells. Although some of the virions formed in induced Friend 745 cells bud into cytoplasmic vesicles that are absent from control cells, this intravesicular budding is not associated with a major increase in the synthesis, processing, or cellular content of virion proteins. MuLV synthesis by Friend 745 cells was compared with that of Ostertag-derived F46/K erythroleukemia cells that produce infectious virus. The synthesis and processing of MuLV-specific proteins were very similar in these independently isolated cell lines, despite the major difference in infectivity of the virus produced.