Differentiation of Mediterranean plum pox virus isolates by coat protein analysis

Six isolates of plum pox potyvirus from different Mediterranean countries were compared by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), peptide mapping and Western blotting after improved purification of virions using a protease inhibitor cocktail that reduced coat protein degradation. One isolate (Spanish isolate 3.3 from plum) differed from the others in possessing a smaller coat protein (approximately 34 instead 36 kDa) with a possible deletion in the surface‐exposed amino‐terminal region. Infectivity of the viruses after proteolysis, assessed using a local lesion host, was significantly reduced. Protease digestion conditions were established to generate a 28 kDa resistant core of the viral coat protein. Such conditions (longer incubation times or an increase in the enzyme concentration) differed from the milder ones reported for other potyviruses. Implications of the results in relation to the production and screening of virus‐specific monoclonal antibodies are discussed.