Genomic cloning and nucleotide sequence analysis of the cDNAs of Tobacco mosaic virus and its mild strains

The genomic RNAs of one virulent strain and two mild strains of Tobacco mosaic virus (TMV) were cloned and sequenced. Results showed that the genomic RNAs of all the three strains were 6 395 nt in length, with 4 open reading frames (ORFs) which encoded proteins of 126, 183, 30 and 17.6 kDa respectively. The nucleotide sequence homology between TMV W (virulent strain) and TMV U1 was 98%, indicating that TMV W was also a common strain. Compared with TMV W, the nucleotide sequence variations of the 2 mild strains (TMV 017 and TMV 152) located mainly in the ORFs of 126 or 183 kDa. In TMV 017, variations only occurred in the ORF of 126 kDa, where 18 nucleotide mutations caused the alteration of 10 amino acids. There were 16 nucleotide mutations in the 183 kDa ORF of TMV 152, 11 of which caused change of predicted proteins. There were 11 common nucleotide mutations in 126 kDa ORFs of TMV 017 and TMV 152, 8 of which caused the alteration of amino acid. In addition, there was 1 nucleotide mutation that caused the alteration of 1 amino acid in 30 kDa ORF of TMV 152 when compared to that of TMV W. The other regions were identical among the three strains.