Coat protein of potyviruses. I. Comparison of the four Australian strains of sugarcane mosaic virus

As an aid to a more rational classification of the potyvirus group, we have examined the molecular weight, amino acid composition, and tryptic peptide map of the coat protein of four Australian sugarcane mosaic virus strains: Johnson grass (JG), sugarcane (SC), Queensland blue couch grass (BC), and sabi grass (Sabi). The proteins migrated as a single band in SDS-polyacrylamide gel electrophoresis with molecular weights of 33,700 (SC), 34,200 (JG), 39,100 (BC), and 40,300 (Sabi). The BC and Sabi strains have identical amino acid compositions and tryptic peptide maps. The SC strain has a similar amino acid composition and tryptic peptide map but these two properties of the JG strain show very little similarity to the three other strains. On the basis of the coat protein properties investigated, we propose that the four sugarcane mosaic virus strains be subdivided into two groups: the sugarcane group containing SC, BC, and the Sabi strains and the Johnson grass group containing the JG strain.