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Electrophoresis patterns of cyanogen bromide (CNBr) peptides from the proteins of the cowpea (SBc), bean (SBb), Mexican (SBm), and Ghana (SBg) strains of southern bean mosaic virus showed a marked similarity between SBc and SBg and between SBb and SBm. A highly basic CNBr peptide from SBc, cCB-1, was isolated by Sephadex and ion-exchange chromatography. The size and amino acid composition of cCB-1 was similar but differed from that of the N-terminal CNBr peptide bCB-1 from SBb described previously.Antisera to cCB-1 or bCB-1 conjugated to tomato bushy stunt virus (TBSV) were used in gel diffusion tests with virus particles of the four SB strains. With the bCB-1–TBSV conjugate antiserum, SBb gave a reaction of identity with SBm and reactions of partial identity with SBc and SBg. With the cCB-1–TBSV conjugate antiserum, SBc gave a reaction of identity with SBg and reactions of partial identity with SBb and SBm. Cross absorption of bCB-1–TBSV conjugate antiserum with TBSV yielded an antiserum that reacted with SBb but not with TBSV. Cross absorption with bCB-1 yielded an antiserum that reacted with TBSV but not with SBb.Limited tryptic proteolysis of SBc in 0.01 M sodium phosphate buffer containing 0.01 M ethylenediaminetetraacetic acid, pH 8.0, resulted in the formation of viruslike particles and smaller spherical particles. Sixteen peptides were isolated from these digests and the compositions of most of them were similar to but not identical to peptides isolated from limited tryptic proteolysis of SBb.

A decline in sporulation noted with cells from cultures aged 7–30 days was not due to a decrease in the proportion of viable cells. The optimum cell population density for sporulation in acetate solution was two to four millions per milliliter and seemed unaffected by acetate concentration. Cells from three presporulation media that allowed moderate growth sporulated poorly in acetate solution. Seven assimilable sugars stimulated sporulation at low concentration in water agar, while three non-assimilable sugars and mannitol did not. Glucose-1-phosphate, fructose-1,6-diphosphate, and sodium aspartate were stimulating. The following were non-stimulating: sodium formate, sodium propionate, propionic acid, sodium oxalate, oxalic acid, sodium citrate, citric acid, aminoacctic acid, glutaric acid, indole-3-acetic acid, acetaldehydc, ethyl alcohol, histamine, glucosamine. Differences are pointed out between the chemical conditions favoring growth and sporulation.

Southern bean mosaic virus (SBMV) protein was cleaved with cyanogen bromide and a highly basic peptide, CB-1, was isolated by ion exclusion and ion-exchange chromatography. Twelve peptides were separated from a tryptic digest of CB-1 by ion-exchange chromatography and the composition of these peptides was similar to that of peptides released from EDTA-swollen virus particles by limited tryptic digestion. The composition and N-termini of the tryptic peptides indicated CB-1 was from the N-terminus of SBMV protein and contained 48 amino acid residues. The CB-1 peptide moved rapidly to the cathode in polyacrylamide gel electrophoresis at pH 3.9 and contained nine arginine residues, three lysine residues, and no acidic amino acid residues. It was shown to interact with purified viral RNA, sodium dextran sulfate, and calf thymus DNA.Antiserum to sodium dodecyl sulfate (SDS)-dissociated virus gave a reaction of partial identity between the CB-1 peptide and the SDS-dissociated virus in SDS gel diffusion tests. The CB-1 peptide did not react with antiserum to SDS-dissociated, trypsin-treated virus. Gel diffusion tests conducted in saline agar gels between trypsin-treated virus and SBMV, with SBMV antiserum, did not show differences in their serological properties. Antiserum to the CB-1 peptide conjugated to tomato bushy stunt virus reacted with SBMV but SBMV antiserum did not react with CB-1 or the CB-1-tomato bushy stunt virus conjugate.

To facilitate the recognition of plant viruses with similar characteristics a dendrogram of characterized viruses was constructed. The sequence of criteria included: type of nucleic acid; single or double stranded; presence or absence of lipid envelope; helical or nonhelical symmetry; and divided or single genome. Nonhelical RNA viruses with divided genomes were further divided into viruses with one or more than one capsid size. Those with one capsid size were subdivided into viruses with one or more than one sedimenting component. Nonhelical RNA viruses with a single genome were divided according to their RNA size, and their sensitivity to sodium dodecyl sulfate and ethyIenediaminetetraacetic acid.