Translation of turnip rosette virus RNA in rabbit reticulocyte lysates

Turnip rosette virus (TRosV) RNA was translated in nuclease-treated rabbit reticulocyte lysates, and four principal products (radioactive proteins always found under routine conditions) with molecular weights of 105,000, 67,000, 35,000, and 30,000 were synthesized. Optimum conditions for translation included 50 mM added K+, no added Mg2+, TRosV RNA at 25 to 50 mug/ml, incubation for 40 to 60 min; these conditions gave 20-fold stimulation in the incorporation of [35S]methionine over endogenous background levels. The 30,000 MW protein was identified as virus capsid protein by peptide mapping of specific immunoprecipitates. Most efficient synthesis of the capsid protein was observed for a virus-encapsidated subgenomic RNA (denatured MW 0.5 x 10(6)). The major genome products of 105,000, 67,000, and 35,000 MW were shown to be related by peptide analysis following partial proteolysis. Time course analyses suggested that the 67,000 product was processed from the 105,000 product by post-translational cleavage. The protease activity responsible for product cleavage was apparently viral coded and protease inhibitor studies further indicated the enzyme was of the thiol type. In an initiation assay using anisomycin, two ribosomes bound per TRosV RNA. The strategy of translation as determined for the virus here is discussed.