Minor protein components in cowpea chlorotic mottle virus and satellite of tobacco necrosis virus

Structure and assembly of turnip crinkle virus. II. Mechanism of reassembly in vitro

Dissociation of turnip crinkle virus (TCV) at elevated pH and ionic strength produces free dimers of the coat protein and a ribonucleoprotein complex that contains the viral RNA, six coat-protein subunits, and the minor protein species, p80 (a covalently linked coat-protein dimer). This "rp-complex" is stable for several days in high salt at pH 8.5. Reassembly of TCV can be accomplished under physiological conditions, using isolated coat protein and either rp-complex or protein-free RNA. If rp-complex is used in reassembly, the same subunits remain bound to RNA on subsequent dissociation; if free RNA is used, rp-complex is regenerated. In both cases, the assembly is selective for viral RNA in competition experiments with heterologous RNA. Electron microscopy shows that assembly proceeds by continuous growth of a shell from an initiating structure, rather than by formation of distinct intermediates. We suggest that rp-complex is the initiating structure, suggest a model based on the organization of the TCV particle, and propose a mechanism for TCV assembly.

Structure of turnip crinkle virus. III. Identification of a unique coat protein dimer

The minor structural protein (p80), found in about one copy per virion in turnip crinkle virus (TCV), is shown by amino acid analysis and peptide mapping to be a covalent dimer of the major coat protein (p40). The covalent linkage occurs near the N termini of the crosslinked chains. These data suggest that TGV and related viruses contain 178 copies of p40 (89 non-covalent dimers) and one copy of p80 (covalent dimer of two additional p40 chains). The presence of p80 in the salt-stable RNA-protein complex formed when TCV dissociates, as described in an accompanying paper, indicates that the covalent modification affects binding to RNA. We suggest that p80 might be the final dimer to be incorporated into the shell and that it might also be the site for initiation of uncoating.

The capsid polypeptides of the yeast viruses

The yeast virus is a double-stranded RNA virus with a large genomic dsRNA and one major viral capsid polypeptide. Most strains of yeast have a major and a minor species of the large genomic dsRNA present. The major species has previously been shown to encode a capsid polypeptide with a Mr of about 88,000. We show that the minor species also encodes its capsid polypeptide with a Mr of about 80,000. Unlike all the dsRNA viruses of procaryotes and higher eucaryotes, the yeast virus appears to have only one major polypeptide in its virions. There are some 60 molecules of this capsid polypeptide per particle, consistent with a simple icosohedron of T=1.

Isolation of galactoprotein a from hamster embryo fibroblasts and characterization of the carbohydrate unit

A major cell surface labeled glycoprotein of hamster embryo fibroblasts, with a subunit molecular weight of 230 000, which is deleted on viral transformation [Gahmberg, C. G., & Hakomori, S. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 3329--3333; Hynes, R. O. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 3170--3174], was quantitatively extracted and purified on an insolubilized Ricinus communis lectin--poly(acrylhydrazido)agarose column. A glycopeptide with a molecular weight of 2000 was isolated from the glycoprotein after exhaustive digestion with protease of Streptomyces griseus. The carbohydrate structure of the isolated glycopeptide was determined, as seen in Figure 7, by carbohydrate analysis, stepwise degradation by exoglycosidases followed by hydrolysis with endo-beta-N-acetylglucosaminidase of Diplococcus pneumoniae, methylation analysis with gas chromatography--mass spectrometry, and direct probe mass spectrometry of the methylated core oligosaccharide, released by endo-beta-N-acetylglucosaminidase.

Isolation and characterization of cyanogen bromide fragments and a glycopeptide from the Dolichos biflorus lectin

The 110000 molecular weight Dolichos biflorus lectin is a glycoprotein composed of four subunits of approximately 27000 molecular weight with one methionine residue per subunit (Carter and Etzler, 1975b). Cyanogen bromide cleavage of the lectin yielded two fragments with approximate molecular weights of 15000 and 12000 as determined by electrophoresis on sodium dodecyl sulfate gels. Only the 15000 molecular weight fragment stained for carbohydrate with the periodic acid-Schiff stain. The two fragments were isolated, and their amino acid compositions were determined. The 15000 molecular weight fragment was identified as the amino terminal segment of the lectin subunits by NH2-terminal amino acid analysis. A glycopeptide with a minimum molecular weight of 1100 was isolated from the lectin by exhaustive Pronase digestion. Complete acid hydrolysis of the glycopeptide yielded aspartic acid, mannose, and N-acetylglucosamine in the ratio of 1:4-5:1-2. Partial acid hydrolysis of the glycopeptide produced a component which had an identical mobility with commercial N-acetylglucosaminylasparagine in high voltage paper electrophoresis. The data indicate that the carbohydrate unit of the lectin is bound to the amino terminal half of the subunits by a glycosylamine linkage between N-acetylglucosamine and asparagine.