Association of the non-structural P3 viral protein with cylindrical inclusions in potyvirus-infected cells

Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546, U.S.A. Antibodies raised against the 42K non-structural P3 protein encoded by the RNA genome of a potyvirus (tobacco vein mottling virus, TVMV) have been used with immunogold labelling procedures to determine the subcellular location of P3 in infected Nicotiana tabacum cells. P3-specific gold label was found almost exclusively associated with the cylindrical inclusions typically formed in the cytoplasm of potyvirus-infected cells by another non-structural viral protein, the cylindrical inclusion protein. The P3 antibodies reacted with inclusions in both the transverse (pinwheel-like) and longitudinal (bundle-like) orientations of these structures. Immunocytological examination of TVMV-infected protoplasts showed the association of P3 with cylindrical inclusions during the early stages of formation of these structures and suggests that the P3 may be involved in the replication of potyviral RNA. Present address: Centro Nacional de Biotecnología-CSIC, Campus Universidad Autónoma, 28049 Madrid, Spain. Received 9 March 1993; accepted 4 May 1993.