The effects of tobacco mosaic virus synthesis on the free amino acid and amide composition of the host.

1. Changes in concentrations of free amino acids and amides have been determined in TMV-infected tobacco leaf discs and in comparable uninfected discs during the time of virus formation. 2. During the period of rapid virus formation the infected discs show a transitory deficiency (as compared to uninfected discs) in glutamine, asparagine, aspartic acid, glutamic acid, serine, and to a lesser extent in valine, threonine, and proline. About 100 hours before this time smaller deficiencies in the concentrations of these components also occur. The latter effect is probably associated with the early synthesis of a non-virus protein in infected tissue. 3. Comparison of the above effects with the known amino acid composition of TMV indicates that it is unlikely that the virus protein is synthesized by condensation of appropriate free amino acids. Rather, the deficiencies observed appear to result from removal of ammonia from the nitrogen pool during synthesis of new proteins in infected tissue. Equilibrium shifts resulting from ammonia withdrawal probably account for the observed deficiencies in amides and free amino acids. TMV protein, therefore, appears to be synthesized de novo, from non-protein nitrogen, probably ammonia. 4. It is suggested that the changes in free amino acid concentrations induced by virus formation may account for some of the symptoms observed in infected plants.