Polypeptide components of virions, top component and cores of reovirus type 3

Studies on the topography of reovirus and bluetongue virus capsid proteins

Protein labeling experiments confirm the surface location of proteins 2 and 5 in bluetongue virus, and proteins sigma3 and mu2 in reovirus. Lambda 2 is the major surface component of the reovirus core, and proteins 1, 3, and 4 appear to be the outer components of the bluetongue virus subviral particle.

Bacteriophage T4 head morphogenesis. Isolation, partial characterization, and fate of gene 21-defective tau-particles

A lysozyme-detergent procedure was developed for isolation of tau-particles from cells infected by gene-21 mutants of T4 bacteriophage. These particles have a sedimentation coefficient of 440 +/- 10 S. They contain less than 1% detectable nuclease-resistant DNA, are smaller (650 x 850 A) than normal bacteriophage heads (800 x 1100 A), and exhibit two major bands on 7.5% Na dodecyl sulfate-acrylamide gels. The more prominent band (55,000 daltons) corresponds to the uncleaved, major capsid polypeptide (P23); the other band (32,000 daltons) corresponds to the gene-22 product (P22). Temperature-shift experiments with cells infected with tsN8 (gene 21) mutants were used to study the fate of tau-particles accumulated under nonpermissive conditions. 50 Min after ts N8-infected cells were shifted from the nonpermissive (41.5 degrees ) to the permissive (25 degrees ) temperature, a phage burst occurred that was 75% of that observed with wild-type phage. However, in "pulse-chase" temperature-shift experiments, the radioactive tau-particle peak only slightly decreased (by 10-14%) by 50 min after the shift, whereas an increased amount of radioactivity (about four times as much as the tau-particle decrease) appeared in phage particles. The results suggest that at least two pools of head polypeptides coexist in cells infected with gene-21 mutants. One pool is composed of head subunits assembled into tau-particles, which are mostly aberrant structures; the second pool is composed of head subunits that are incorporated into mature phage when the gene-21 product becomes functional.

Early events in cell-animal virus interactions

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Properties of a 5'-nucleotidase purified from mouse liver plasma membranes

1. Extraction of a mouse liver plasma-membrane fraction with a detergent buffer, N-dodecylsarcosinate-Tris buffer (sarcosyl-Tris buffer), solubilized 90% of the protein and 70% of the 5'-nucleotidase activity. 2. The proteins of the sarcosyl-Tris buffer extract were fractionated by a rate-zonal centrifugation in a sucrose-detergent gradient. The major protein peak sedimented ahead of phospholipids, which mainly remained in the overlay. Glycoproteins were separated ahead of the protein peak. 3. The 5'-nucleotidase activity peak was associated with 5% of the protein applied to the gradient, and contained relatively few protein bands. 4. The 5'-nucleotidase was purified further by gel filtration on Sepharose and Sephadex columns equilibrated with sarcosyl-Tris buffer, to give a single glycoprotein band on sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The purified enzyme was lipid-free. 5. Electrophoresis in polyacrylamide gels in sarcosyl-Tris buffers showed that the enzymic activity was coincident with the protein band. 6. The molecular weight suggested for the enzyme activity by gel filtration or centrifugation in sucrose gradients was 140000-150000. Sometimes, a minor enzyme peak of lower molecular weight was obtained. 7. Polyacrylamide-gel electrophoresis in sodium dodecyl sulphate indicated that as the polyacrylamide concentration was increased from 5 to 15%, the apparent molecular weight of the enzyme decreased from 130000 to 90000. 8. The evidence that 5'-nucleotidase is composed of two active and similar, if not identical, glycoprotein subunits and the role of detergent in effecting the separation of membrane proteins and glycoproteins are discussed. 9. Substrate requirements, pH optima and the nature of inhibition by an analogue of adenosine diphosphate are reported.

The effect of poly-L-lysine on the uptake of reovirus double-stranded RNA in macrophages in vitro

The effect of polycations on cultured mouse peitoneal macrophages has been examined. Polycations, at concentrations greater than 5 microg/ml, are toxic for macrophages) as measured by failure of the cells to exclude vital dyes. At toxic concentrations polycations bind in large amounts to nuclei and endoplasmic reticulum, while at nontoxic levels polycations bind selectively to the cell surface. Nontoxic concentrations of polycations stimulate binding of reovirus double-stranded (ds) RNA to the macrophages by forming polycation-dsRNA complexes either in the medium or at the cell surface. These complexes enter the cell in endocytic vacuoles and are concentrated in secondary lysosomes. Despite exposure to the acid hydrolases within this cell compartment, the dsRNA and the polycation (poly-L-lysine) are conserved in a macromolecular form within the vacuolar system. The mechanism(s) by which the uptake of infectious nucleic acids and the induction of interferon by dsRNA are stimulated by polycations are discussed.

New intermediate subviral particles in the in vitro uncoating of reovirus virions by chymotrypsin

Reovirus virions, grown in suspension cultures of L cells and extensively purified by density gradient and velocity gradient centrifugation after their release from cell debris by fluorocarbon extraction, are characterized by a mean particle diameter of 73 nm and a density in CsCl of 1.36 to 1.37 g/cm(3). Treatment of intact virions by chymotrypsin (CHT) digestion in vitro converts them to subviral particles (SVP) having characteristics which are determined by the species of monovalent cation present during the digestion. In the presence of Cs(+) ions, CHT converts the virions to SVP of mean diameter 51 nm and density 1.43 to 1.44 g/cm(3). In the presence of K(+) ions, the conversion is to SVP of diameter 51 nm and density 1.39 to 1.40 g/cm(3). The SVP made in the presence of either Cs(+) or K(+) possess an extremely active RNA polymerase and nucleoside triphosphate phosphohydrolase (NTPase) activity in vitro and are resistant to further digestion by CHT. Treatment of intact virions with CHT in the presence of Na(+) or Li(+) ions results in their conversion to SVP of mean diameter 64 nm and density 1.37 to 1.38 g/cm(3). Such SVP are not active in in vitro RNA synthesis or NTP hydrolysis and are resistant to further digestion by CHT even during prolonged exposure to high concentrations of enzyme. Addition of Cs(+) or K(+) ions to the digestion mixture allows conversion of the 64-nm diameter SVP to 51-nm diameter SVP in which the RNA polymerase and NTPase are active in vitro. Analysis of the proteins present in intact virions and in the different SVP reveals clear differences which indicate that the conversions are accomplished by removal or cleavage of particular species of polypeptides.

Production and purification of large amounts of Rous sarcoma virus

Procedures are described for production and purification of large amounts of Rous sarcoma virus. The virus was produced by Rous sarcoma virus-transformed chicken embryo fibroblasts in roller culture which produced up to 6 mg of virus per day per liter of supernatant fluid. Various methods of concentrating virus were evaluated; pelleting yielded the best results in terms of recovery of infectious virus. Purification was achieved by means of successive velocity and equilibrium density centrifugation by using sucrose solutions made in low-salt buffer. A rapid method for the optical density measurement of virus concentration was also developed.

Physiocochemical studies on L-cell virions

The L-cell virion (LCV) has been purified from supernatant fluids of mouse L cells grown in suspension culture. The virion is similar to other RNA tumor viruses by several criteria: (i) the density of the virion is 1.16 g/cm(3); (ii) the virion appears as a rounded membranous particle with an outer diameter of 146.7 +/- 11.8 nm, and contains knobs (7-nm diameter) over its surface; (iii) 15 polypeptides (ranging in molecular weight from 7,000 to 110,000) are detectable after electrophoresis of virion protein in sodium dodecyl sulfate-polyacrylamide gels; (iv) three species of RNA can be isolated-high molecular weight (80 to 88s) (50%), 7s (35%) and 4s (15%); (v) heat denaturation of the high-molecular-weight RNA yields a heterogeneous population of molecules (20 to 35s) as well as a 7s and 4s species. Despite the general similarity to infectious RNA tumor viruses, LCV is apparently defective as evidenced by the fact that it does not induce tumors in animals or transform normal mouse cells in vitro (Kindig and Kirsten [17]). The defective nature of the LCV might be related to the fact that assays for DNA polymerase in the virion showed only a negligible activity when compared to Rous sarcoma virus.

Reovirus: effect of noninfective viral components on cellular deoxyribonucleic acid synthesis

We determined the effects of noninfective reovirus components on cellular deoxyribonucleic acid (DNA) synthesis. Reovirus inactivated by ultraviolet light inhibited cellular DNA synthesis, whereas reovirus cores and empty capsids did not. Both cores and empty capsids were adsorbed to cells. Adenine-rich ribonucleic acid (RNA) from reovirus, adsorbed to cells in the presence of diethyl-aminoethyl-dextran, produced a partial inhibition of DNA synthesis. RNA was synthesized in the presence of actinomycin D after infection with ultraviolet light-irradiated reovirus, and this RNA synthesis was not due to multiplicity reactivation of virus infectivity. These data suggest that viral structural proteins do not inhibit DNA synthesis and that the inhibition produced by ultraviolet-irradiated virus may be mediated in part or in toto by a newly synthesized viral product.

Extraordinary effects of specific monovalent cations on activation of reovirus transcriptase by chymotrypsin in vitro

Activation of reovirus transcriptase activity, latent in intact virions, by digestion of purified virions with chymotrypsin (CHT) in vitro shows a stringent requirement for specific monovalent cations. Cs(+), Rb(+), or K(+) ions are capable of facilitating activation by chymotryptic digestion. Na(+), Li(+), or NH(4) (+) ions are not capable of facilitating the CHT activation of polymerase activity and are antagonistic towards the effects of the facilitating ions. The data indicate that the effect of the cations is exerted on activation of the polymerase activity by CHT as opposed to an effect on polymerization per se. This effect may be important biologically in that it provides a mechanism whereby the virion can sense whether it is in an intracellular or an extracellular environment and thereby can avoid premature uncoating.

Comparison of the structure and polypeptide composition of three double-stranded ribonucleic acid-containing viruses (diplornaviruses): cytoplasmic polyhedrosis virus, wound tumor virus, and reovirus

Iodination of reovirus, cytoplasmic polyhedrosis virus (CPV), and wound tumor virus (WTV), and their respective subviral forms, followed by analysis of the labeled polypeptides by using polyacrylamide gel electrophoresis, has been used to compare the protein contents of these three diplornaviruses. This approach, when combined with electron microscopy and buoyant density determinations, appears capable of localizing individual polypeptides in some of the viral and subviral forms. CPV (p = 1.435 g/cm(3)) seems to resemble reovirus cores (p = 1.440 g/cm(3)) in both ultrastructure and polypeptide composition. CPV is composed of five polypeptides with molecular weights of about 151,000, 142,000, 130,000, 67,000, and 33,000. The polyhedral matrix, which in nature encapsulates the virions, is, in turn, composed mainly of two polypeptide species with molecular weights of about 30,000 and 20,000, and several minor proteins. The proteins of WTV consist mainly of four species of polypeptide with molecular weights of about 156,000, 122,000, 63,000, and 44,000, and several minor components. These molecular weight determinations are consistent with the hypothesis that, as has been suggested for reovirus, the viral proteins of CPV and WTV seem to be coded for by monocistronic mes senger RNA molecules transcribed from distinct segments of the double-stranded RNA viral genomes.

Transcription by infectious subviral particles of reovirus

Digestion of purified reovirus with chymotrypsin in the presence of 0.15 M NaCl converts virions to infectious subviral particles (SVP(i)). The SVP(i) have an active ribonucleic acid (RNA) polymerase and are similar in composition to the partially uncoated virions which have been isolated from infected L cells. SVP(i) have a buoyant density of 1.40 g/ml in CsCl and sediment at 420S as compared to 1.37 g/ml and 630S for virions. They consist of 30% less protein and include the polypeptides of the inner structural layer, lambda(1), lambda(2), and sigma(3), and a polypeptide derived by cleavage of mu(2), a constituent of the outer shell. The genome RNA is retained within SVP(i), but more than 60% of the "adenine-rich," single-stranded RNA is released by the proteolytic treatment. Infection of L cells with SVP(i) or virions results in the transcription of all 10 genome segments. In cycloheximide-treated SVP(i)-infected cells, transcription occurs predominantly from one medium and two small genome segments, the same pattern of early messenger RNA (mRNA) observed in virion-infected cells. In contrast, SVP(i) incubated in vitro synthesize mRNA corresponding to all genome segments.

Structure of the bluetongue virus capsid

Seven polypeptides were found to be present in the capsid of the bluetongue virus (BTV), four of which are major and three are minor components. This number and size distribution is the same as that found in reovirus, which has a similar segmented, double-stranded ribonucleic acid genome. In both viruses an excellent correlation is found between the molecular weights of certain genome segments and those of the polypeptides, suggesting a direct coding relationship between them. Careful comparison, however, indicates that the correlation patterns of the two viruses are different, suggesting that different genome segments may be utilized to code for certain capsid proteins. This phenomenon may be related to the fact that these viruses can be distinguished morphologically, reovirus having a larger diameter and possessing a double-layered capsid against the smaller single capsid of the BTV. Utilizing the degrading effect of CsCl gradients, it was demonstrated, however, that two of the BTV polypeptides are present as a diffuse protein layer surrounding the capsid. This outer layer probably has some of the functions of the reovirus outer capsid, one being the "masking" of a viral transcriptase which could be demonstrated after its removal.

Translation of reovirus messenger RNAs synthetesized in vitro into reovirus polypeptides by several mammalian cell-free extracts

Single-stranded reovirus RNA, synthesized in vitro by reovirus cores, functioned as messenger RNA in cell-free extracts prepared from several mammalian cells: Krebs II mouse ascites cells, mouse L cells, Chinese hamster ovary cells, HeLa cells, and rabbit reticulocytes. As shown by acrylamide gel electrophoresis, all eight polypeptides known to be specified by reovirus were synthesized in the reticulocyte system. In the other extracts, from 5 to 7 complete virus proteins were made.

Bacteriophage T4 head morphogenesis. IV. Comparison of gene 16-, 17-, and 49-defective head structures

Defective heads present in extracts of bacteriophage T4 gene 16, 17, or 49 mutant-infected cells have been characterized. All appeared as empty shells when examined by negative-stain electron microscopy and showed essentially the same polypeptide pattern on sodium dodecyl sulfate-acrylamide gels. However, when analyzed by several other methods, gene 16- and 17-defective heads were shown to differ markedly from phage heads present in gene 49-defective extracts. First, the gene 16- and 17-defective structures were found to possess a large number of attached tails (50%, rather than about 5%). Second, they contained less nuclease-resistant deoxyribonucleic acid (DNA) (3 versus 18% of a phage equivalent), had a smaller sedimentation coefficient (240 versus 315S), and a lighter density (1.31 vs. 1.34 g/ml) than gene 49-defective heads. Third, they were not attached to the intracellular DNA pool through a deoxyribonuclease-sensitive linkage. Finally, 8-nm diameter capsomers were clearly revealed on the surface of many gene 16- and 17-defective structures. There was a total of 305 +/- 25 capsomers per particle, which yielded an approximate molecular weight of 84 x 10(6) for these heads. The capsomers were presumably not seen on gene 49-defective heads because of the large amount (18%) of associated DNA. These results support the contention that gene 16- and 17-defective heads, in contrast to gene 49-defective structures, represent abortive rather than intermediate structures in T4 head morphogenesis.

Characterization of the polypeptides formed in response to encephalomyocarditis virus ribonucleic acid in a cell-free system from mouse ascites tumor cells

The polypeptide products synthesized at different times in a cell-free system from Krebs mouse ascites tumor cells in response to the addition of encephalomyocarditis (EMC) virus ribonucleic acid (RNA) were characterized by electrophoresis on polyacrylamide gels and fingerprint analysis of their tryptic peptides. Translation of the EMC RNA genome with time occurred in a nonrandom fashion in these systems, to yield products containing sequences characteristic of both virion capsid polypeptides and EMC-specific polypeptides present only in the infected cell. The molecular weights of the products fell in a series from 20,000 to 140,000 daltons, although occasionally traces of larger polypeptides were also observed. All of the major polypeptides appeared to arise from partial or complete translation of about 60% of the EMC RNA genome. They were not formed by cleavage of a large precursor molecule. It is suggested that they are artifacts generated by premature "termination" of nascent polypeptide chains at preferred sites.

Preparation and properties of nexuses and lipid-enriched vesicles from mouse liver plasma membranes

Extraction of mouse liver plasma membranes with 4% (w/v) N-laurylsarcosinate-tris buffer, pH7.8, solubilized 80-90% of the protein and 60% of the 5'-nucleotidase activity. The membrane residue remaining after extraction was resolved on sucrose gradients into two fractions: a vesicular membrane fraction and a fraction characterized by the presence of large numbers of nexuses in an amorphous background. The vesicular fraction had a phospholipid/protein weight ratio of 7:1, it contained most of the plasma-membrane glycolipids, and polyacrylamide-gel electrophoresis indicated the presence of only five to eight proteins, including two or three glycoproteins. The 5'-nucleotidase and leucine naphthylamidase specific activities were 23- and 6-fold higher respectively than in the plasma membranes. Electron microscopy of thin sections and negatively stained preparations indicated that the nexuses present in the second fraction closely resembled gap junctions present in tissue sections and isolated plasma membranes. The nexus fraction contained a distinctive protein pattern, and of the 20 proteins present about four were identified as glycoproteins by Schiff-periodate staining. Examination of the lipid composition of the fractions by t.l.c. showed that in the nexus fraction, phospholipids and glycolipids were present in small amounts compared with triglycerides and cholesterol. Amino sugar analyses confirmed the t.l.c. results and amino acid analysis showed the fractions to have characteristic protein compositions. A ;reconstituted' membranous fraction prepared by dialysis against MgCl(2) of membrane components soluble in N-laurylsarcosinate-tris buffers, pH7.8, lacked the trilaminar image characteristic of the two other membrane fractions isolated and was devoid of enzyme activities. The results indicate that proteins and glycoproteins play an important role in the structural maintenance of the nexuses isolated from the liver by the present procedure.

Reovirus-specific ribonucleic acid from polysomes of infected L cells

Polysomes from reovirus-infected L cells were analyzed. Although all 10 transcription products of the viral genome were represented in polysomes and presumably can be translated, fewer than 10 reovirus-specific polypeptides were detected in infected cells. The 5'-terminal sequence of all species of reovirus ribonucleic acid (RNA) from polysomes was ppGpYp, as previously found for the genome double-stranded RNA and the in vitro single-stranded products of the virion-associated RNA polymerase. RNA isolated from both heavy (>30 ribosomes) and light (5 to 8 ribosomes) polysomes includes similar amounts of large, medium, and small classes of reovirus single-stranded RNA, suggesting that linkage of the genome segments observed in virions may occur at the single-strand stage of RNA replication.

Mechanism of reovirus double-stranded ribonucleic acid synthesis in vivo and in vitro

The complementary strands of reovirus double-stranded ribonucleic acid (ds RNA) are synthesized sequentially in vivo and in vitro. In both cases, preformed plus strands serve as templates for the synthesis of the complementary minus strands. The in vitro synthesis of dsRNA is catalyzed by a large particulate fraction from reovirus-infected cells. Treatment of this fraction with chymotrypsin or with detergents which solubilize cellular membranes does not alter its capacity to synthesize dsRNA. The enzyme or enzymes responsible for dsRNA synthesis remain sedimentable at 10,000 x g after these enzyme or detergent treatments, indicating their particulate nature. Pretreatment of this fraction with ribonuclease, however, abolishes its ability to catalyze dsRNA synthesis, emphasizing the single-stranded nature of the template and its location in a structure permeable to ribonuclease. In contrast, the newly formed dsRNA is resistant to ribonuclease digestion at low salt concentrations and hence is thought to reside within a ribonuclease-impermeable structure.