Assembly of a rod-shaped virus. Disk aggregate of cucumber green mottle mosaic virus protein and its function

Nucleotide sequence of the coat protein cistron and the 3' noncoding region of cucumber green mottle mosaic virus (watermelon strain) RNA

Double-stranded cDNA copies of cucumber green mottle mosaic virus (watermelon strain, CGMMV-W) RNA polyadenylated in vitro were cloned into the pBR322 at the PstI site. The sequence of 1071 nucleotides from the Tend of the genomic RNA was determined using two recombinant plasmids and the genomic RNA. The coat protein cistron was located in residues 176-661 from the 3' end. The coat protein was composed of 160 amino acid residues with the molecular weight of 17,261. The 3' noncoding region of the CGMMVW genome was 175 nucleotides long and highly homologous to that of the common strain of TMV. The assembly origin of reconstitution is positioned within the coat protein cistron as predicted previously. In the 5' flanking region of the coat protein cistron a long open frame, probably of 30K protein, was found. The predicted 30K and the coat protein cistron would overlap each other as is the case of the cowpea strain of TMV.

Structural analysis of A-protein of cucumber green mottle mosaic virus and tobacco mosaic virus by synchrotron small-angle X-ray scattering

The size and shape of A-protein of tobacco mosaic virus coat protein (TMVP) and cucumber green mottle mosaic virus coat protein (CGMMVP) were evaluated by means of small-angle X-ray scattering (SAXS) using a synchrotron radiation source, complemented by electron microscopic observations. The results imply that TMV and CGMMV A-proteins are composed of three and two subunits, respectively, stacked in the shape of an isosceles triangular prism at lower ionic strength. Considering the difference of the A-protein structure at higher and lower ionic strength, the globular core structure was proposed as a subunit which might be modeled as a thin isosceles triangular prism composed of four globular cores joined by rather flexible segments. These cores correspond probably to four helical regions in a subunit, and rearrange their relative positions according to the external conditions. A slight rearrangement of core positions in a subunit may result in the formation of A-proteins of various shapes.

Properties of the coat protein of a new tobacco mosaic virus coat protein ts-mutant

Amino acid substitutions in a majority of tobacco mosaic virus (TMV) coat protein (CP) ts-mutants have previously been mapped to the same region of the CP molecule tertiary structure, located at a distance of about 70 A from TMV virion axis. In the present work some properties of a new TMV CP ts-mutant ts21-66 (two substitutions I21=>T and D66=>G, both in the 70-A region) were studied. Thermal inactivation characteristics, sedimentation properties, circular dichroism spectra, and modification by a lysine-specific reagent, trinitrobenzensulfonic acid, of ts21-66 CP were compared with those of wild-type (U1) TMV CP. It is concluded that the 70-A region represents the most labile portion of the TMV CP molecule. Partial disordering of this region in the mutant CP at permissive temperatures leads to loss of the capacity to form two-layer aggregates of the cylindrical type, while further disordering induced by mild heating results also in the loss of the ability to form ordered helical aggregates.

Mechanism of tobacco mosaic virus assembly: role of subunit and larger aggregate protein

Tobacco mosaic virus (TMV) was reconstituted from the RNA of a common strain (OM) and the protein of a watermelon strain of cucumber green mottle mosaic virus (CGMMV-W), which is a member of the tobamovirus group. In 0.25 M phosphate buffer at 25 degrees C, CGMMV-W protein existed mainly as 21S aggregates. When this protein was mixed with OM RNA, complexes of short rods were formed but further elongation did not occur. After the addition of subunits in 0.1 M phosphate buffer at 25 degrees C, elongation to the 5' end of the RNA proceeded as fast as in the case of reconstitution with the usual equilibrium "disk preparation" of OM protein, to give 260-nm intermediates in the first 5-7 min. The results proved that the rapid elongation we previously observed in the reconstitution of TMV-OM following the assembly initiation is the outcome of preferential incorporation of TMV subunit protein. Either preformed 21S aggregate or the subunit of CGMMV protein was added to the 260-nm intermediate. Elongation to the 3' end of the RNA was investigated in 0.1 M phosphate buffer at 25 degrees C by measuring the distribution of rod length and the RNase-resistant infectivity. The results showed that the 21S aggregate is kinetically favored as the protein source during the slow elongation process.