Abstract: To test the hypothesis and prediction that transgenic coat protein (CP) could recoat the uncoated virions, an epitope tag approach was exploited to look for the exchange of coat protein subunits at the 5' end of the challenged virus. By mutagenesis using a PCR based method, DNA sequences, encoding peptide epitopes (11 and 15 amino acids in length) of the murine hepatitis virus (MHV) S protein were separately inserted into one of the two sites near the 3' end of the coded region of the TMV CP gene. Two TMV infections clones with each of the tagged coat protein genes, V9 (tl amino acids) and El5 (15 amino acids) were generated. Viral RNA was produced by in vitro transcription with T7 RNA polymerase and used to infect Xanthi nn and Xanthi NN tobacco plants. BothV9 and El5 caused local necrotic lesion in NN tobacco plants similar to those induced by wild type TMV. Systemic symptoms identical to those caused by TMV-U1 infection and equivalent amounts of coat protein with the MHV epitope (El5) were found in Xanthi nn tobacco plants. Unexpectedly, similar types of local lesions were observed on the inoculated leaves of Xanthi nn tobacco plants infected by V9. The different sites of insertion of each MHV epitope may be responsible for the different characteristics of V9 and El5.

Key words: Transgenic plants, Coat protein, Tobacco mosaic virus, Epitope tag, Murine hepatitis virus