Evidence for intramolecular self-cleavage of picornaviral replicase precursors

Abstract
When encephalomyocarditis viral RNA is translated in rabbit reticulocyte cell-free extracts, it synthesizes a virus-coded protease, p22, which is derived by cleavage of a precursor protein, C. Protein C is shown here to cleaved by 2 different mechanisms, one sensitive to dilution and the other insensitive. The biphasic cleavage behavior was unchanged by diluting incubation mixtures with untranslated reticulocyte extract instead of buffer, suggesting that both types of cleavage were mediated by virus translation products. Evidently the dilution-sensitive cleavage of protein C is due to a virus-coded protease, probably p22 itself, and the dilution-independent cleavage is due to intramolecular self-cleavage of protein C.