Reinvestigation of intracellular localization of the 30K protein in tobacco protoplasts infected with tobacco mosaic virus RNA.

It has been shown that the 30K protein of tobacco mosaic virus (TMV) is responsible for the cell-to-cell movement function of the virus. It is still obscure how the protein is involved in this function at the molecular level. We formerly found that the 30K protein is localized to the plasmodesmata of TMV-infected plants. We also reported that the 30K protein was detected in a nuclei-rich fraction of TMV-infected protoplasts after biochemical fractionation. To clarify the inconsistency, the 30K protein was immunocytologically localized in TMV-infected protoplasts using a newly prepared antibody against the 30K protein. On some sections, the 30K protein was found near the nucleus but not in or on the nucleus. At later stages of infection a novel electron-transparent structure was detected in the cytoplasm where the 30K proteins were localized. This structure might reflect an intermediate form between its synthesis in the cytoplasm and its targeting to the plasmodesmata in whole plants.