Molecular weights of plant virus coat proteins by polyacrylamide gel electrophoresis

Studies on encapsidated viroid-like RNA I. Characterization of velvet tobacco mottle virus

Velvet tobacco mottle virus (VTMoV) isolated from Nicotiana velutina growing wild in arid Central Australia was transmitted by inoculation to a limited number of plant species of which N. clevelandii was the most convenient experimental host. The virus was also transmitted from field-grown plants toN. velutina and N. clevelandii by the mirid Cyropeltis nicotianae. VTMoV preparations purified by clarification with organic solvents and differential centrifugation contained polyhedral particles about 30 nm in diameter sedimenting as a single component at about 115 S. The particles were shown to be located in the nucleus, cytoplasm, and vacuoles of infected plant cells. Virus dissociated in the presence of mercaptoethanol and sodium dodecyl sulfate (SDS) separated into one major and two minor polypeptides with estimated molecular weights of 33,000, 36,000 and 31,000, respectively. Single-stranded RNA isolated from VTMoV by extraction with phenol was separated into five components with apparent molecular weights of 1.5 x 10(6), 0.63 x 10(6), 0.25 x 10(6), 0.16 x 10(6), and 0.12 x 10(6) referred to as RNAs 1, 1a, 1b, 2, and 3, respectively. It appears that RNAs 1a and 1b are breakdown products of RNA 1, as shown elsewhere, and electron microscopic examination of the other species showed that whereas RNAs 1 and 3 are linear molecules, RNA 2 is circular. The similarity of RNAs 2 and 3 to the RNA of viroids is discussed. VTMoV has been compared with several RNA plant viruses with small polyhedral particles. Only solanum nodiflorum mottle virus appears to share some of its unique features and the two have been shown to be antigenically related.

The conserved, hydrophilic and arginine-rich N-terminal domain of cucumovirus coat proteins contributes to their anomalous electrophoretic mobilities in sodium dodecylsulfate-polyacrylamide gels

Although the Mr values of the coat proteins (CPs) of several cucumoviruses have been calculated from their deduced amino acid sequences to be approximately 24,000, the experimentally determined M(r) values using the Laemmli SDS-PAGE system were 30,000-31,000. Examination of the amino acid composition revealed that these CPs are neither highly acidic nor highly basic. Post-translational glycosylation or phosphorylation were also ruled out as contributing factors to the observed anomalous electrophoretic mobility because the products of in vitro translation of cucumovirus RNA 4 and in vivo bacterial expression of the cloned CP gene co-migrated with authentic cucumovirus CPs. Comparison of the hydropathy profiles of the CPs revealed the presence in each of a strikingly similar, highly hydrophilic N-terminal domain of 30-32 amino acid residues that contains a cluster of basic amino acids, mainly arginine. Selective chemical cleavage at tryptophan residues in the CPs of cucumoviruses, known to contain single tryptophan residues, yielded two peptides; an N-terminal peptide that contained the conserved hydrophilic domain and a C-terminal peptide. SDS-PAGE analysis showed that the N-terminal, but not the C-terminal, peptide exhibited the anomalous electrophoretic mobility.