THE 119-KDA AND 124-KDA POLYPROTEINS OF ARABIS MOSAIC NEPOVIRUS (ISOLATE-S) ARE ENCODED BY 2 DISTINCT RNA2 SPECIES

Arabis mosaic virus (ArMV) is a nepovirus that is serologically distan tly related to grapevine fanleaf virus (GFLV). Both ArMV and GFLV indu ce grapevine degeneration disease. Several ArMV isolates, unlike isola tes of GFLV, produce upon in vitro translation of RNA2 a polyprotein ( P2) that forms a double band in polyacrylamide-SDS gels. Cloning of fu ll-length copies of RNA2 of an ArMV isolate from grapevine (ArMV-S) re vealed that this isolate contained two RNA2s of different length, call ed RNA2-U and RNA2-L. The two species were not readily separated by el ectrophoresis of the virion RNA under denaturing gel electrophoresis c onditions but could be distinguished by analysis of primer extension a nd in vitro translation products. The size difference of the two RNA2s is due mostly if not exclusively to differences in their coding regio ns. The 124 kDa RNA2-U-encoded polyprotein P2' and the 119 kDa RNA2-L- encoded polyprotein P2'', which comigrate, respectively, with the uppe r and lower polyprotein bands produced by RNA2 of ArMV-S, were more th an 95% identical except in their N-terminal domains. In vitro maturati on experiments and sequence comparisons indicate that the N-terminal p roducts of P2' and P2'' have a molecular mass of 31 kDa and 26 kDa. Th e genomic organization proposed is similar to that of GFLV RNA2.