Tritium labeling for investigation of structure-function relationship in tobacco mosaic virus

The catalytic thermal dissociation of tritium gas on a hot tungsten wire is the convenient way for generation of atomic tritium. During the bombardment of solid targets by tritium atoms from gas phase labeling takes place in the thin surface layer. This phenomenon is used for structural investigations of biological objects. In the present work intact virions of tobacco mosaic virus (wild strain U1 and mutant ts21-66, which has two substitutions in the amino acid sequence of the coat protein and is characterized by temperature sensibility and ability to induce necroses on some plant hosts) were exposed to atomic tritium labeling for determination of differences in the organization of coat proteins in virus particles. After labeling and purification the wild-type and mutant coat proteins were hydrolyzed by trypsin and specific radioactivity of individual amino acid residues in each peptide was determined. Several reliable differences in intramolecular tritium distribution in the tobacco mosaic virus coat proteins were found and their relationship to some changes in mutant coat protein higher order structure which can lead to changes in function is discussed.