Cultured feline lymphoma cells (FL-74), productively infected with a feline leukaemia virus (FeLV) were quantitatively examined with a radioimmune assay for cell membrane associated FeLV-p27 and total FeLV associated cell surface antigens (FeLV-CSA) using a monospecific antiserum and a broadly reactive antiserum respectively. The infected cells bound 5.6 × 10 anti-FeLV-p27 IgG molecules/cell, representing 40% of the total FeLV-CSA detected. The kinetics of synthesis of surface associated p27 and total FeLV-CSA was determined following their removal by treatment of intact cells with trypsin. Both p27 and the total FeLV-CSA population reappeared on the cell surface within 6 to 8 h following trypsin digestion. Antigen re-expression was blocked by cycloheximide but not by actinomycin D or cordycepin. The time course of antigen decay with these same antimetabolites indicated that the average turnover rate of cell surface p27 and FeLV-CSA was 6 to 8 h while the mRNAs which specify these antigens have a lifetime of at least 10 h. Virus production was blocked in less than 2 h by cycloheximide, and within 2 to 4 h by actinomycin D. Virus production continued at a reduced rate for at least 6 h in the presence of cordycepin. The difference in sensitivity to inhibitors of RNA synthesis of p27 and FeLV-CSA production (blocked in 9 to 10 h) and of virus production (blocked in 2 to 4 h) supports the proposition of two non-equilibrating pools of intracellular virus RNA molecules with different half-lives: one associated with polyribosomes, and another which becomes encapsulated in the completed virion.


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