The Purification and Properties of One of the ‘b’ Proteins from Virus-Infected Tobacco Plants

The b1 protein, produced in leaves of Nicotiana tabacum cv. Xanthi-nc following infection with tobacco mosaic virus, has been purified to homogeneity by a procedure which involves gel chromatography and absorption on to DEAE-cellulose. One gel chromatography step was sufficient when the procedure was applied to leaf extracts made in an acid buffer, whereas two were necessary with extracts made at pH 8. The final product migrates as a single protein band on electrophoresis in both acrylamide and SDS-acrylamide gels. Its mol. wt. is estimated to be 15000 by electrophoresis and 14200 by ultracentrifugation. Amino acid analysis suggests that it contains about 136 residues of which 39 are potentially acidic, 13 basic and 16 aromatic. The absorbance coefficient A 1% 280 nm is estimated to be 18.9. No evidence was found for the presence of a nucleotide component.