Cotranslational disassembly of a cowpea strain (Cc) of TMV: evidence that viral RNA-protein interactions at the assembly origin block ribosome translocation in vitro.

Cotranslational disassembly of mixed rod-length populations of tobacco mosaic virus (TMV; vulgare, common or, U1 strain), reveals a reproducible, significant reduction in the level of expression of the intermediate-sized, subgenomic 12-RNA when compared with conventional total viral RNA preparations. I2-RNA encodes a 30-kDa protein, and recent evidence suggests that I2-RNA is unusual in that it lacks a 5'-cap structure. In TMV vulgare, the assembly origin is located within the 30-kDa protein-coding region. To resolve which of these structural features might be responsible for the decline in 30-kDa gene expression from packaged 12-RNAs, the products encoded in vitro by packaged or naked genomic and subgenomic RNAs from two strains of TMV, vulgare and a cowpea strain (Cc or Sunn-hemp mosaic virus), were compared. The results indicate that strong coat protein-RNA interactions, presumed to occur at the assembly origin, dictate the site at which translocation of 80 S ribosomes is inhibited. The implications of this conclusion for virus infection in vivo are discussed.