Potato virus X coat protein: a glycoprotein.

The coat protein (CP) genes of all the strains of potato virus X (PVX) code for a protein of 25 kDa. Analysis of the CP by SDS-PAGE shows a migration mobility of 27 to 29 kDa, depending of the strain. Amino acid identity between some strains is too high to explain such abnormal migration by differences in primary structure of the protein. Periodate oxidation demonstrated the presence of carbohydrate moieties in purified CP of six PVX strains (cp, CP4, HB, MS, DX, CS35), and trifluoromethanesulfonic acid treatment identified glycosylated and nonglycosylated bands in SDS-PAGE complex patterns of CP and in Western blots. Digestion with glycosidases, recognition by lectins, and mild alkali treatment (beta-elimination) of PVX CP indicated the presence of an O-linked sugar.