A circular dichroism study of the interaction of adenylic acid oligo- and polynucleotides with TMV protein

Coordinated two-disk nucleation, growth and properties, of virus-like particles assembled from tobacco-mosaic-virus capsid protein with poly(A) or oligo(A) of different length

Assembly of nucleoprotein rods from tobacco mosaic virus (TMV) coat protein and poly(A) depends on the presence of 20S disks in a manner very similar to nucleation and growth of virions in reconstitution with TMV RNA. Products assembled with (A) approximately equal to 5000 appear to have the same buoyant density in CsCl, the same nucleotide/protein ratio and the same nuclease stability, as reconstituted and native TMV. Their rate of formation is very similar to the rate of reconstitution with TMV RNA when high-molecular-mass (A) approximately equal to 5000 is used, but becomes a function of chain length particularly with (A) less than or equal to 185. The composition of assembly products can be described sufficiently with the relation between number of capsid polypeptide monomers/particle, np, to the number of nucleotide residues/chain, nnt, of np = 1/3 (nnt + 50) with two important restrictions: (1) particles of less than four turns of helically arranged capsid subunits are unstable, and (2) particles with about 150 or less nucleotides per chain deviate in structure from mature virus and virus-like (= longer) assembly products. This is indicated by changes in both buoyant density in CsCl and optical properties, while 'dislocation' of the disk to the helical arrangement of capsid subunits ('helicalization') and nuclease stability already become established with chains as short as (A) approximately equal to 58 +/- 20. Consequently, we suggest that assembly proceeds through three distinct phases: (1) nucleation (resulting in helicalization) by interaction of nucleic acid with the first disk; (2) stabilization of the primary (unstable!) nucleation complex by addition of a second disk and formation of a four-turn virus-like and stable nucleoprotein helix, which is then fit for (3) elongation by addition of further disks. The question of what makes the TMV protein disk select specifically TMV RNA during virion assembly is discussed in some detail.

Mechanism of RNA-protein interactions in tobacco mosaic virus: analysis of the pH stability of virus protein complexes with synthetic polynucleotides

TMV-like RNP complexes were reconstituted from TMV protein and synthetic polynucleotides. Analysis of the pH stability of RNP with polynucleotides containing U, G, or their analogues reveals a correlation between the stability of their structure and the pK values of the bases, and indicates that the -NH-CO-groups of U and G are involved in hydrogen bonding with protein. It is suggested that TMV protein has two U- and one G-specific binding sites which, according to the phase position of the protein subunits relative to the origin of TMV assembly (D. Zimmern (1977), Cell 11, 463) are likely to be organized as UGU. The binding of the A and C residues of RNA with TMV protein is nonspecific. TMV protein groups with pK 6.3, 7.5 and 9.7 were found to be essential in the protein-protein interactions in RNP. A group of the protein with pK 8.2 is also involved in RNP stabilization. Both protein-protein interactions and interactions of protein with RNA phosphate groups were shown to be mediated by a conformational change in the protein induced by base binding. The effect of bases on both types of interactions changes in the order G approximately equal to much greater than A, and incorporation of C in RNP proceeds in a compulsory way at the expense of interaction of the neighbouring nucleotide residues in polynucleotides with protein. The data obtained are used to discuss the principles of the cooperativity of the interactions between TMV components and the mechanism of initiation and elongation in TMV self-assembly.

Structure of single-stranded virus RNA in situ. II. Optical activity of five tobacco mosaic-like viruses and their components

ORD and CD spectra of some TM-like viruses and their coat proteins were measured to study a possible role of tryptophan residues in RNA-protein interactions in these viruses. Five viruses of this group, differing in tryptophan content of their coat proteins, were used: v-TM virus (3 tryptophan residues per protein subunit), strains HR and U2 (2 tryptophan residues per subunit), dolihos enation mosaic virus and cucumber virus 4(1 tryptophan residue per subunit). The viruses differ significantly in their ORD and CD spectra and some correlation between these spectra and tryptophan content of coat proteins seems to exist. But an analysis of "intravirus RNA" CD spectra, obtained by subtraction of CD spectra of virus -like protein assemblies from the spectra of intact viruses, shows that the observed differences in optical activity can hardly be explained by tryptophan participation in RNA-protein interactions. The presence of the "additional" peak at 293 nm in the ORD of TM virus had been considered as evidence of tryptophan-RNA interactions in this virus. In the present work such a peak at 293 nm was observed in the ORD of all the 5 viruses studied, irrespective of the tryptophan content in their coat proteins. Besides, we managed to obtain the virus-like protein assemblies preparations which also showed a peak at 293 nm. All these data show that, in all probability, the 293 nm peak in the ORD of TM virus does not result from tryptophan-RNA interactions. It is believed that the difference in the optical activity of RNA particles of TM-like viruses do originate from the differences in the RNA-protein interactions in these viruses, but these interactions can hardly involve tryptophan residues of virus coat proteins.