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Cricket paralysis virus purified from Galleria mellonella larvae was shown to be similar to virus purified from Drosophila melanogaster cells. Cricket paralysis virus contained three major structural polypeptides of similar molecular weight (around 30,000), had a buoyant density of 1.344 g/ml, and had a capsid diameter of 27 nm. Twenty virus-induced polypeptides could be detected in CrPV-infected Drosophila cells. Two major polypeptides found in the infected cells corresponded to two structural viral polypeptides (VP1 and VP3), whereas the third major intracellular polypeptide was the apparent precursor of the third viral structural polypeptide (VP2). Three of the primary virus-induced polypeptides had molecular weights of 144,000, 124,000, and 115,000. These and other polypeptides were chased into lower-molecular-weight proteins when excess cold methionine was added after a short [ 35 S]methionine pulse. Although cricket paralysis virus has a number of characteristics in common with the mammalian enteroviruses, the extremely fast processing of high-molecular-weight polypeptides into viral proteins seems atypical. Also, no VP4 (8,000 to 10,000 molecular weight) has been found in the virus particles.

Infection of Drosophila cells with Cricket paralysis virus in the presence of Actinomycin D results in virtual complete inhibition of host cell protein synthesis by four hours post-infection. Using 35S-methionine or 14C-amino acids to pulse infected cells three major classes of viral induced proteins can be detected, (A) high molecular weight precursor proteins, (B) viral structural proteins and (C) low molecular weight cleavage products. The large number of high molecular weight proteins found in the infected cells suggests that a multiple cleavage cascade mechanism is partially utilized to produce virus structural proteins. In infected cells, even with short pulses, the largest viral induced protein obtained has a molecular weight of 144,000. However with pretreatment of the infected cells with iodoacetamide before pulsing, two further proteins are obtained with molecular weights of 205,000 and 190,000. Other changes occur in viral protein precursors in the presence of iodoacetamide.

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