PRIMARY STRUCTURE AND SEQUENCE-ANALYSIS OF RNA2 OF A MECHANICALLY TRANSMITTED BARLEY MILD MOSAIC-VIRUS ISOLATE - AN EVOLUTIONARY RELATIONSHIP BETWEEN BYMOVIRUSES AND FUROVIRUSES

The RNA2 nucleotide sequence of a mechanically transmitted isolate of barley mild mosaic virus (BaMMV) has been determined. A combination of Northern blot and sequence analysis indicates that this RNA2 lacks approximately 1000 nucleotides of its C-terminal protein (P2) gene, with respect to Polymyxa graminis transmitted BaMMV. This is confirmed by sequence comparison with RNA2 of a fungus transmitted BaMMV isolate, which reveals the presence of a single deletion located in the 3'-terminal part of the P2 gene. As a consequence, this RNA2 codes for a P2 protein of only 34 K. Sequence homology between the bymovirus P2 protein and the capsid readthrough protein of beet necrotic yellow vein virus and soil-borne wheat mosaic virus suggests an evolutionary relationship between bymo- and furoviruses.