Abstract: Broad bean wilt virus 2 (BBWV2) isolate P158 was characterized and the complete nucleotide sequence of viral genomic RNA2 was determined. P158 has 30 nm diameter isometric particles. Double immunodiffusion test suggested that P158 has high antigenicity homology with BBWV2 isolate B935. SDS-PAGE result showed that the coat protein of P158 was comprised of two types of polypeptide with molecular weight of 44.7 kD and 21.9 kD, respectively. The genome of P158 was made up of two RNA molecules with the length of 6.0 kb and 3.6 kb, respectively. cDNA of RNA2 was cloned by RT-PCR and sequenced. RNA2 was composed of 3597 nucleotide (nt) residues excluding the poly(A) tail and contained single long open reading frame extending from nt 230 to nt 3424 in the viral sense RNA, and encoded a polyprotein of Mr 119002 (119K). Comparison of the polyprotein and the counterpart of isolate B935 indicated that the polyprotein was cleaved at Q/G (465/466) and Q/A (867/868), to release three mature proteins: a protein of unknown function, large and small subunit. Sequence comparisons of P158 with fabaviruses showed P158 had very high sequence homology with BBWV2 isolates and patchouli mild mosaic virus, but to a less extent with BBWV1 isolates.

Key words: broad bean wilt virus, characterization, RNA2 sequence

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