ULTRASTRUCTURAL-LOCALIZATION OF NONSTRUCTURAL AND COAT PROTEINS OF 19POTYVIRUSES USING ANTISERA TO BACTERIALLY EXPRESSED PROTEINS OF PLUM POX POTYVIRUS

Antisera to the bacterially expressed nonstructural proteins (NSP) HC- Pro, CI, NIa, and NIb and the coat protein (CP) of plum pox potyvirus (PPV) were used for analysing the composition of virus-induced cytopla smic and nuclear inclusions by electron microscopy. The antisera react ed with NSP and CP of PPV on immunogold-labelled ultrathin sections. A ntiserum to CP reacted with virions of seven out of 18 other potyvirus es. CP was distributed throughout the cytoplasm of infected cells. Ant isera to PPV NSP specifically reacted with virus-specific cytoplasmic and/or nuclear inclusions induced by 17 different potyviruses. NSP wer e furthermore localized in confined cytoplasmic areas in between compl ex accumulations of virus-specific inclusions. Cylindrical inclusions induced by the potyviruses were proven to consist of CI protein. Most other cytoplasmic or nuclear inclusions were shown to be composed of t wo or more NSP. An unexpected composition of virus-induced inclusions was observed for the crystalline nuclear inclusions of tobacco etch vi rus. Here, in addition to the expected presence of NIa and NIb, HC-Pro could be demonstrated. Furthermore, amorphous cytoplasmic inclusions induced by papaya ringspot virus contained the expected HC-Pro but add itionally NIa, NIb and CI. Beet mosaic virus-induced nuclear inclusion s ('satellite bodies') contained in their electron-dense matrix NIa, N Ib, Hc-Pro and CI and in their lacunae CP in bundles of virion-like fi laments. The results indicate that all cytoplasmic or nuclear inclusio ns of potyviruses have to be regarded as deposition sites of excessive ly produced viral NSP.