STRUCTURE OF TOBACCO NECROSIS VIRUS .2. TERMINAL AMINO ACID RESIDUES OF PROTEIN SUBUNIT

The amino end group of the protein of tobacco necrosis virus (TNV), unlike those of most other plant viruses, was found to be unsubstituted. Reactions with fluorodinitrobenzene and 1-dimethylaminonaphthalene-5-sulfonyl chloride (dansyl) resulted in the identification of alanine as the amino terminal residue. Leucine aminopeptidase, at slightly alkaline pH, released up to 62% of the theoretical value of alanine from the whole virus. The TNV coat protein N-terminus is therefore identical to that of its satellite and the RNA-containing bacteriophages. Kinetic studies with carboxypeptidase suggested that the C-terminal sequence of tobacco necrosis virus coat protein is ...Ser·Val·Val·Met. Quantitative end-group analysis was in agreement with the earlier suggested molecular weight of the protein subunit as 33,300. The number of tryptic peptides separated on fingerprints was also consistent with these data. © 1969.