In Vivo Localization of Ubiquitin in Tobacco Mosaic Virus Infected and Uninfected Tobacco Cells. José O. Gaspar. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. David D. Dunigan, and Milton Zaitlin. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 3:182-187. Accepted 3 January 1990. Copyright 1990 The American Phytopathological Society.

A small proportion of the coat protein subunits in virions of tobacco mosaic virus (TMV) have been shown to be ubiquitinated (D. D. Dunigan, R. G. Dietzgen, J. E. Schoelz, and M. Zaitlin, Virology 165:310-312, 1988). To determine if there was specific ubiquitination of virus-infected tissues, an analysis of both TMV-infected and uninfected tobacco tissues was made by an immunogold-labeling technique using polyclonal antiserum to human ubiquitin. Colloidal gold labeling, indicating the presence of ubiquitin and/or ubiquitin conjugates, was found in the cytoplasmic matrix, chloroplasts, nucleus, and nucleolus equivalently in both healthy leaf tissue and leaf tissue infected with TMV. Cell walls and vacuoles were not labeled. In virus-infected cells, the ribbonlike structures contained within viroplasms were tagged by the anti-ubiquitin antibodies. These ribbons contain the 126K TMV putative replicase protein (G. J. Hills, K. A. Plaskitt, N. D. Young, D. D. Dunigan, J. W. Watts, T. M. A. Wilson, and M. Zaitlin, Virology 161:488-496, 1987). TMV particle aggregates in tissues were not labeled by this technique, and neither were purified TMV virions.