Viral protein synthesis in Friend erythroleukemia cell lines

Viral protein synthesis was studied in 2 Friend virus induced erythroleukemia cell lines (Ostertag cell lines FSD1 F4 and B8) by the technique of immunoprecipitation with monospecific antisera to the major envelope glycoprotein gp70 and major core protein p30. One of the cell lines (F4) releases active Friend virus complex to the growth medium, where release of virus from the other cell line (B8) is barely or nondetectable. It was found that in the nonproducer cell line B8, a large molecular weight protein of about 65,000 containing p30 antigenic determinants is synthesized, yet no p30 is produced upon prolonged incubation and chase, suggesting that this might be the actual lesion that prevents mature virus production by these cells. In both cell lines, the predominant protein species that is immunoprecipitated with monospecific anti gp70 serum is a protein of 55,000 to 60,000 daltons that is labeled with glucosamine to a much lesser extent than gp70 and appears to become heterogeneous with time. Large amounts of gp70 can be detected in the cell free medium, but none of the unstable species of 55,000 to 60,000 molecular weight.