Comparison of Three Pathogenesis-related Proteins from Plants of Two Cultivars of Tobacco Infected with TMV

A procedure is described for purifying the b1, b2 and b3 proteins from leaves of Nicotiana tabacum cv. Xanthi-nc, a cultivar reacting hypersensitively to tobacco mosaic virus (TMV). All three proteins consist of a single polypeptide, have similar mol. wt. of about 14200 but differ in charge. In contrast, the b4 protein differs from b1 to b3 in both charge and size. The same procedure purifies the proteins IV, III and II from TMV-infected leaves of N. tabacum cv. Samsun NN. The Samsun NN proteins IV to II resemble the b1 to b3 proteins from Xanthi-nc in electrophoretic mobility in polyacrylamide gels and in mol. wt.; b1, IV and III have similar amino acid compositions.

It is suggested that these proteins be called pathogenesis-related proteins (PRs) and a unified system of nomenclature is proposed which groups similar proteins.