An isolateof the Southern bean mosaic virus (SBMV), genus Sobemovirus, found in the State of São Paulo, Brazil, was purified and some of its molecular properties determined. The virus particles are 28-30 nm in diameter and the coat protein has a molecular mass of 30 kDa. A heterogeneous population of RNAs (4.2 Kb, 3.1 Kb, 2.65 Kb, 2.15 Kb, 1.64 Kb, 1.36 Kb and 1.0 Kb) was extracted from virus particles, where those of 4.2 Kb and 1.0 Kb are, respectively, the genomic and the putative subgenomic RNA for coat protein. RNAs of the same size were also extracted from infected common bean (Phaseolus vulgaris) leaves, indicating that they must have some function in the virus replication cycle. Only two species of double-stranded RNAs (dsRNA) were extracted from infected tissues (4.2 Kbp and 1.0 Kbp), corresponding to the replicative forms of the genomic RNA and the subgenomic RNA for coat protein. These results indicate that only these two RNAs replicate by means of replicative forms (RF) while the others are probably synthesized by an internal initiation of the negative strand of the genomic RNA. The SBMV-B SP showed molecular properties analogous to the SBMV described in North America.
