The predicted amino acid sequences of the polyproteins of two potyviruses, tobacco vein mottling virus (TVMV) and tobacco etch virus (TEV), were compared to each other, to proteins of other viruses, and to the National Biomedical Research Foundation protein sequence bank. Three potyviral proteins, the cylindrical inclusion and the two nuclear inclusion proteins, were found to be homologous to proteins considered to be involved in the replication and expression of picorna- and comovirus RNA. A lower, but also significant, level of homology was observed between a putative N-terminal 28-kDa protein of TVMV, the 30-kDa protein of tobacco mosaic virus, and the 29-kDa protein of tobacco rattle virus, the latter two of which are thought to be involved in cell-to-cell movement of virus or viral RNA. The aphid transmission helper component of TVMV was homologous to the aphid transmission factors of two strains of cauliflower mosaic virus. A region of the putative TEV polyprotein, located between the helper component and the cylindrical inclusion protein, contained a sequence that was homologous to the conserved region of the 2A protease of picornaviruses. These results suggest functions for all of the potyviral proteins and also indicate that poty-, como-, and picornaviruses may share a similar replication strategy and genome organization.
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