The cell-free synthesis and assembly of viral specific polypeptides into TMV particles

In a cell-free system derived from wheat germ, the ribonucleic acid of the tobacco mosaic virus mutant Ni 568 directs the synthesis of polypeptides with molecular weights from 10,000 to 140,000, but there is little synthesis of a product equal in size to the coat protein. However, further incubation of the cell-free products with or without extracts from tobacco leaves resulted in the appearance of ³⁵S methionine labeled polypeptides comigrating with tobacco mosaic virus coat protein on sodium dodecyl sulfate-acrylamide gels. Tobacco mosaic virus particles assembled in the presence of these treated cell-free products were shown to be radioactive and co-banded with authentic tobacco mosaic virus during equilibrium centrifugation in cesium chloride. Upon dissociation the assembled particles were found to contain several labeled polypeptides, the most prominent of which comigrated with tobacco mosaic virus coat protein on sodium dodecyl sulfate-acrylamide gels. Furthermore tryptic digests of these polypeptides contained a ³⁵S-methionine labeled peptide with a mobility during high voltage paper ionophoresis at pH 6.5 precisely coincident with that of the only methionine-containing peptide in the coat protein.