The Tobacco Mosaic Virus Genome: Organization and Gene Function

Abstract

Tobacco mosaic virus (TMV) RNA codes for at least 4 polypeptides, only one of which, the coat protein, has a known function. Evidence is presented that one of these proteins (30 K protein) may be involved in potentiating the cell-to-cell movement of the virus in the plant. Virions of TMV also contain an average of one molecule of another protein (H protein) in addition to the 2130 molecules of coat protein. H protein is postulated to be an unusual branched molecule, containing the coat protein plus an additional peptide moiety of either host or viral origin. Analyses of single-stranded and double-stranded RNAs found in TMV-infected tissue by gel electrophoresis, blotting and hybridization revealed the presence of the genomic TMV and its double-stranded replicative form, and 9 subgenomic mRNAs, at least three of which also had double-stranded forms. Low molecular weight TMV-related RNAs representing different regions of the genome were also observed to arise during virus replication. Sequences derived from a number of TMV strains have confirmed strain relationships previously established, and the arrangement of the four TMV genes and have suggested the presence of other genes. Moreover, the sequence data indicate that several of the genes overlap, both in the same reading frame and in different reading frames.