Synthesis and processing of viral proteins in Friend erythroleukemia cell lines

The synthesis and processing of viral proteins in a number of Friend erythroleukemia cell lines were characterized by the use of monospecific antisera to purified viral structural proteins. In all cell lines studied, a major intracellular species precipitated with anti-gp69/71 serum was a protein of 55,000 MW. This 55,000 MW protein was detectable after a 5-min pulse, along with the 85,000 MW glycoprotein precursor to gp69/71, suggesting that it might be a primary translation product. The major glycoprotein gp69/71 was only observed after a 30-min chase period. Analysis of pulse-labeled cell extracts with monospecific antisera to the core proteins p12, p15, and p30 revealed the presence of viral specific proteins intermediate in size between the gag precursor polyprotein and the mature viral proteins. These intermediate species probably represent processing intermediates, and an analysis of their antigenic specificities was in agreement with the core protein arrangement, p15-p12-p30-p10, within the gag polyprotein precursor. Under conditions where more membrane-associated material was extracted, a 180,000 MW species precipitable with antiserum against p30 as well as anti-reverse transcriptase serum was observed. Alterations in viral precursor processing were observed in the Friend cell lines during the chemically induced differentiation process.