Some tryptic peptides of bromovirus proteins

The action of trypsin on brome mosaic virus (BMV) at pH 8 resulted in the dissociation of the virus particles into an 8 S component which contained two proteins, I and F. Protein I was capable of reassembly at pH 8 or 5 into 16-nm spherical particles; protein F formed these particles only at pH 5. SDS-polyacrylamide-gel electrophoresis and amino acid analysis indicated that protein F was about 23 and protein I about 18 amino acid residues smaller than native BMV protein. Six peptides, a cleavage product of the acetylated N-terminal peptide, free arginine, and eight other peptides containing more than one basic amino acid were isolated and their amino acid compositions and N-terminal residues were determined. The BMV peptides were similar or identical to peptides isolated after the limited proteolysis of cowpea chlorotic mottle virus protein at the N-terminus. The sequences of these portions of both viral proteins are probably very similar and probably function as sites of RNA-protein interaction. Peptides isolated from a total tryptic digestion of broad bean mottle virus protein were unlike peptides cleaved in limited proteolysis of BMV and cowpea chlorotic mottle virus