Characterization of alfalfa-mosaic-virus protein polymerization in the presence of nucleic acid

The polymerization of alfalfa mosaic virus (AMV) protein in the presence of homologous nucleic acids and a number of other natural and synthetic nucleic acids was studied. The conditions for optimal assembly were found to be pH 6.0 and low ionic strength (I = 0.1 M) at room temperature, irrespective of the type of nucleic acid. The resulting nucleoprotein particles exhibited the same structural characteristics as the virus. This information emerged from optical diffraction and computer filtering of electron micrographs from the reconstituted particles. Irrespective of the type of nucleic acid present the polymerization of the protein resulting in a nucleoprotein particle is a cooperative process. Evidence for this was obtained by nitrocellulose filter binding assay, sodium dodecylsulphate/polyacrylamide gel electrophoresis, sedimentation velocity and electron microscopy of the reaction mixtures. The rates and efficiencies of reconstitution were of the same order of magnitude for a number of ribonucleic acids. Sedimentation data derived from AMV protein and AMV RNA mixtures suggested the existence of a specific nucleation product in the first stage of assembly. The results are discussed in terms of a tentative model of the assembly, in which at least two different steps (nucleation and elongation) can be distinguished, each characterized by an association constant.

Determination of the sequence homology between the four RNA species of cucumber mosaic virus by hybridization analysis with complementary DNA

The method of Taylor etal., (11) has been used to transcribe complementary DNA probes from the four major RNA species of cucumber mosaic virus (RNAs 1 - 4 in order of decreasing molecular weight). Analysis of the kinetics of hybridization of these probes in homologous and heterologous complementary DNA-RNA hybridization reactions has shown that the sequence of the smallest RNA (RNA 4), which contains the coat protein gene, is present within RNA 3. RNAs 1 and 2 are unique RNA molecules while each has a region of approximately 300 nucleotides in common with RNA 4.Images

Cell surface labelling of mononuclear cells with antisera associated to turnip yellow mosaic virus of alphalpha mosaic virus particles. A freeze-etch study

Turnip yellow mosaic virus (TYMV) and alphalpha mosaic virus (AMV) were used as immuno-electron microscopical markers to detect cell surface receptors on mononuclear cells in freeze-etch replicas. TYMV particles were conjugated with vacuum-distilled glutaraldehyde to rabbit IgG anti-mouse immunoglobulins (TYMV-RAMIg conjugate) or to rabbit IgG anti-mouse theta antigen (TYMV-RAMTh conjugate). B-lymphocytes incubated with TYMV-RAMIg conjugate showed either randomly distributed particles or patches of virus particles on the etched surface of the cell membrane. Mouse thymocytes incubated with TYMV-RAMTh conjugate, however, showed only a random distribution of the virus particles. Human mononuclear cells incubated with rabbit IgG anti-AMV and AMV for the demonstration of the receptors for the Fc fragment of IgG showed the oblong shape of the AMV particles on the etched cell membrane, Fc receptors were either randomly distributed or aggregrated into patches. It is concluded that both types of virus particles are useful markers for the demonstration of membrane receptors in freeze-etch replicas of labelled cells.

Monocistronic translation of alfalfa mosaic virus RNAs

The four alfalfa mosaic virus RNAs (respectively 24 S, 20 S, 17 S and 12 S) have been used separately as messengers in two in vitro protein synthesizing systems: wheat germ and rabbit reticulocyte lysate. In both systems a polypeptide corresponding to the translation of the entire length of the RNA can be found for RNAs 24 S, 20 S and 12 S, but not for 17 S RNA, the translation product of which is only 35,000 daltons. The number of initiation sites has been determined for each RNA by analyzing the initiation peptides synthesized in the presence of spasomycin and show that there is only one initiation or binding site perRNA. We thus conclude that each AMV RNA behaves as a monocistronic messenger in in vitro translating systems.

Protein expression in E. coli minicells by recombinant plasmids

The polypeptides synthesized in E. coli minicells from recombinant plasmids containing DNA fragments from cauliflower mosaic virus, Drosophila melanogaster, and mouse mitochondria were examined. Molecularly cloned fragments of cauliflower mosaic virus DNA directed the synthesis of high levels of three polypeptides, which were synthesized entirely from within the cloned virus DNA fragments independent of their insertion into the plasmid vehicles. Several fragments of D. melanogaster DNA were capable of initiating polypeptide synthesis; however, termination of these polypeptides was dependent upon the insertion into the plasmid vehicle. The majority of D. melanogaster DNA fragments examined did not direct the detectable synthesis of any polypeptides. Insertion of DNA into the Eco RI site of ColE1 and pSC101 plasmids resulted in the altered expression of plasmid-encoded polypeptides. In the case of ColE1, this site of insertion lies within the colicin E1 structural gene, and insertion of foreign DNA into the site results in the synthesis of an inactive truncated colicin E1 molecule. It is probable that the Eco RI site in pSC101 lies within the structural gene for a polypeptide involved in tetracycline resistance, and insertion of DNA into this site may also result in the synthesis of a truncated or elongated polypeptide.

Quasi-elastic behavior of solutions of viral capsid and RNA at very low shearing stresses

By the application of shearing stresses on the order of 10(-3) dyne cm-2 (10(-2) muN cm-2), via the magnetic viscodensimeter, extremely high relative viscosities (greater than 500) were observed when turnip yellow mosaic virus was degraded in alkali into its capsid and RNA. The solutions, however, possessed a watery consistency at this stage and exhibited a quasi-elastic character by rotor-recoil experiments. The development of this curious behavior was concentration and temperature dependent; it was not seen less than 0.5% nor at 8 degrees, and appeared sooner at 30 degrees than at 20 degrees. The time of appearance was delayed as the pH was lowered; however, the effect was still observed when the pH was as low as 9. Whereas reversibility was demonstrated when the shearing stresses exceeded the elastic resistance [0.17 dyne cm-2 (1.7 muN CM-2)], thorough mixing usually resulted in a normal behavior of the solutions thereafter. Values for the modulus of rigidity at 20 degrees for about 1% virus concentration was less than 2 X 10(-2) dyne cm-2 rad-1 (0.2 muN cm-2 rad-1), which, while extremely small, was reproducible. A porous structure, possibly involving a capsid and RNA complex, is envisioned.

Ultrastructural pathology of leaf cells of ryegrass (Lolium multiflorum) infected with ryegrass mosaic virus

Ryegrass mosaic virus particles and virus induced lamellar inclusions were found in mesophyll and epidermal cells of virus infected ryegrass leaves. The lamellar inclusions were occasionally found in phloem cells also. Virus particles occurred in cytoplasm, inside plasmodesmata and often in membrane bound sacs embedded in a matrix between plasmalemma and cell wall at or near plasmodesmata. Electron dense plugs protruding from plasmodesmata, finger-like cell wall outgrowths and cell wall deposits usually at plasmodesmata were also observed. Cytopathological changes in organelles in infected cells included dense deposits in the cisternae of endosplasmic reticulum and Golgi apparatus, mitochondria with electron-dense or opaque matrix, proliferating cristae and deteriorating unit membrane; and disintegrating chloroplasts.

Barley stripe mosaic virions assoicated with spindle microtubules

Virions of barley stripe mosaic virus were observed attached to microtubules of the spindle apparatus. This phenomenon was found in barley cells undergoing meiosis and mitosis. The microtubules may be involved in the assembly and cell-to-cell transfer of the virus.