Evidence for in vitro and in vivo autocatalytic processing of the primary translation product of beet necrotic yellow vein virus RNA 1 by a papain-like proteinase

Beet necrotic yellow vein virus RNA 1 contains a single long ORF corresponding to the theoretical translation product of 237 kDa which contains the information necessary for replication of the viral genome. This ORF contains a putative papain-like proteinase domain which has been localized, on the basis of sequence alignments, between the helicase and polymerase domains. Here we show that the RNA 1 primary translation product can be cleaved autocatalytically in vitro into two species of 150 kDa and 66 kDa, the latter of which probably contains the entire polymerase domain. A 66 kDa protein was detected immunologically in infected C. quinoa protoplasts using an antiserum specific for the C-terminal region of the RNA 1 primary translation product, confirming that processing also occurs in vivo.