EVIDENCE FOR IN-VITRO AND IN-VIVO AUTOCATALYTIC PROCESSING OF THE PRIMARY TRANSLATION PRODUCT OF BEET NECROTIC YELLOW VEIN VIRUS-RNA-1 BY APAPAIN-LIKE PROTEINASE

Beet necrotic yellow vein virus RNA 1 contains a single long ORF corre sponding to the theoretical translation product of 237 kDa which conta ins the information necessary for replication of the viral genome. Thi s 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 translatio n product can be cleaved autocatalytically in vitro into two species o f 150 kDa and 66 kDa, the latter of which probably contains the entire polymerase domain. A 66 kDa protein was detected immunologically in i nfected C. quinoa protoplasts using an antiserum specific for the C-te rminal region of the RNA 1 primary translation product, confirming tha t processing also occurs in vivo.