ACCUMULATION KINETICS OF CMV RNA-3-ENCODED PROTEINS AND SUBCELLULAR-LOCALIZATION OF THE 3A PROTEIN IN INFECTED AND TRANSGENIC TOBACCO PLANTS

The complete nucleotide sequence of RNA 3 of a Spanish isolate of cucu mber mosaic virus (CMV-24) has been determined. The encoded putative c ell-to-cell movement protein (3a protein) and the coat protein are 279 and 218 amino acids long, respectively. The 3a protein was expressed in Escherichia coli using the vector pT7-7 and was used to raise an im munoserum. We have followed the time course of accumulation of the 3a protein, in parallel to that of the coat protein, and its subcellular localization as a function of time after CMV-24 infection on tobacco p lants. The maximum accumulation level of the 3a protein was reached at early stages of infection, being detected in the cytosolic and the ce ll wall fractions. At later stages of infection, a decline in accumula tion levels of the 3a protein was observed, and the protein was essent ially associated with the cell wall fractions. These data were corrobo rated by immunocytochemistry performed in both infected and 3a-express ing transgenic tobacco plants.