The effect of sodium thiocyanate on virus structure

Features of the 3'-consensus sequence of rotavirus mRNAs critical to minus strand synthesis

The last seven nucleotides of the 3'-end of rotavirus mRNAs, 5'-UGUGACC-3', are highly conserved and form a cis-acting signal that can promote the synthesis of (-) strand RNA to produce the viral dsRNA genome in vitro. Previous studies have shown that the sequence, location, and strandedness (single- versus double-stranded) of the 3'-consensus sequence of the mRNA affect the efficiency of (-) strand synthesis. In this study, we have used exhaustive mutagenesis of the SA11 gene 8 mRNA and an in vitro replication system to define the importance of each of the residues in the consensus sequence in (-) strand synthesis. The analysis showed that the CC of the consensus sequence was the most critical for (-) strand synthesis. Furthermore, the data revealed that other, but not all, residues of the consensus sequence contributed to efficient (-) strand synthesis in vitro. Mutant gene 8 RNAs supported an intermediate level of (-) strand synthesis when the 15 nt sequence upstream of the CC was replaced with long tracts of poly(A) or poly(U), but not with poly(G). Predictions of the secondary structure of the mutant RNAs suggested that the poly(G)-RNA could not replicate because its 3'-terminus was largely basepaired, instead of extending as a single-stranded tail as is the case for the 3'-termini of the poly(A)- and poly(U)-RNAs and wild-type gene 8 RNA. Subsequent experiments performed with complementary oligonucleotides indicated that efficient RNA replication occurs in vitro only when the last four residues of the 3'-consensus sequence, and most importantly the two terminal C's, existed in a single-stranded form. A single-stranded CC may be crucial for formation of an initiation complex for (-) strand synthesis consisting of viral RdRP, mRNA, and the dinucleotide pGpG.

The rotavirus genus

Human rotaviruses, discovered nearly 20 years ago, have been proven to be major cause of paediatric diarrhoeal disease morbidity and mortality. The clinical significance of these viruses stimulated basic studies on their biology, molecular and antigenic properties and epidemiology. General features, clinical relevance, epidemiologic pattern and laboratory diagnosis of human rotavirus infections are here reviewed.

Sigma 1 protein of mammalian reoviruses extends from the surfaces of viral particles

Electron microscopy revealed structures consisting of long fibers topped with knobs extending from the surfaces of virions of mammalian reoviruses. The morphology of these structures was reminiscent of the fiber protein of adenovirus. Fibers were also seen extending from the reovirus top component and intermediate subviral particles but not from cores, suggesting that the fibers consist of either the mu 1C or sigma 1 outer capsid protein. Amino acid sequence analysis predicts that the reovirus cell attachment protein sigma 1 contains an extended fiber domain (R. Bassel-Duby, A. Jayasuriya, D. Chatterjee, N. Sonenberg, J. V. Maizell, Jr., and B. N. Fields, Nature [London] 315:421-423, 1985). When sigma 1 protein was released from viral particles with mild heat and subsequently obtained in isolation, it was found to have a morphology identical to that of the fiber structures seen extending from the viral particles. The identification of an extended form of sigma 1 has important implications for its function in cell attachment. Other evidence suggests that sigma 1 protein may occur in virions in both an extended and an unextended state.

Uncoating of parental bluetongue virus to core and subcore particles in infected L cells

A study was made of the fate of parental bluetongue virus (BTV) in infected cells. Within the first hour after infection, the BTV particles are converted to core particles with the loss of major capsid polypeptides P2 and P5. The particles are able to synthesize mRNA in vitro in a transcription reaction characterized by a temperature-dependent inhibition at high core concentrations. From about 6 hr after infection a second uncoating event is observed in which the 470 S core particles are converted to 390 S subcore particles. These particles are morphologically strikingly different from core particles and have a skeletonlike structure with a hexagonal profile and a side to side diameter of 40 nm. These subcore particles contain only one major structural protein, P3, and three minor proteins, P1, P4, and P6. They do, however, contain all 10 double-stranded RNA segments. The results suggest that the characteristic capsomeres on the surface of core particles are composed mainly of P7, the soluble group-specific antigen of BTV. The subcore particles are stable only at very low salt concentrations. Under these conditions no transcriptase activity can be demonstrated.

In vitro assembly of bovine rotavirus nucleocapsid protein

The nucleocapsid protein (VP6) of bovine rotavirus was purified from in vitro-derived single shelled particles by CaCl2 or LiCl treatment. The protein exhibits polymorphism. Specifically, hexamers and small hexagonal lattices were present in many of the samples. Tubular particles formed between pH 5.0 and 9.0 were moderately stable to changes in temperature and ionic strength and were shown to be composed of nucleocapsid protein. Their formation is fully reversible. Spherical particles resembling single-shelled virus formed at pH 4.0. A novel structure in the form of sheets composed of a small-hole lattice formed in samples shifted from pH 6.0 to 4.0. The results demonstrate the importance of the nucleocapsid protein and of protein-protein interactions for rotavirus assembly.

Congophilia in cerebral amyloidosis is modified by inactivation procedures on slow transmissible pathogens

Cerebral tissues with amyloid deposits were treated by various chemicals which inactivated the agent of subacute spongiform encephalopathy (SSE). We discovered Congophilia in the amyloid plaques in cases of Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler syndrome (GSS) correlated to the chemical inactivation profiles of SSE. After incubation with trichloroacetate, guanidine-SCN, guanidine-HCl, formic acid, phenol and autoclaving, amyloid plaques in unfixed frozen sections of human brains with CJD or GSS, lost the affinity of Congo red and green birefringence under polarized light. In formalin-fixed, paraffin-embedded tissue sections, amyloid plaques of CJD and GSS lost the affinity of Congo red after most of these treatments. On the other hand, senile plaques in the aged, patients with Alzheimer's disease and with senile dementia of the Alzheimer type did not lose the affinity of Congo red after most of these treatments. Therefore, the amyloid deposits in the amyloid plaques differ from those in senile plaques. The methods we used facilitate differentiation of amyloid and senile plaques in formalin-fixed, paraffin-embedded tissues.

Role of the inner protein capsid on in vitro human rotavirus transcription

The inner protein shell of human rotavirus consists of a single polypeptide called VP6 which was removed from the single-shelled virus by treatment with CaCl2, leaving the viral core. The core thus obtained was unable to transcribe. However, the addition of a supernatant containing VP6 in the absence of Ca2+ restored the transcriptional activity. VP6 obtained from different electropherotypes and serotypes was able to restore transcriptional activity to homologous and heterologous cores. Viral cores obtained after incubation with purified VP6 had electron microscopic characteristics, polypeptide compositions, and transcription products similar to those of the single-shelled virus. The results suggested the successful in vitro reconstitution of the single-shelled virus.

Porcine rotavirus-like virus (group B rotavirus): characterization and pathogenicity for gnotobiotic pigs

A rotavirus-like virus (RVLV) was isolated from a diarrheic pig from an Ohio swine herd. This virus infected villous enterocytes throughout the small intestine of gnotobiotic pigs and induced an acute, transitory diarrhea. Complete virions were rarely observed in the intestinal contents of infected animals; the predominant particle detected by immune electron microscopy was a corelike particle 52 nm in diameter. The genome of the porcine RVLV was composed of 11 discrete segments of double-stranded RNA that produced an electropherotype distinct from the genome electropherotypes of reovirus, rotavirus, and porcine pararotavirus. Porcine RVLV was antigenically unrelated to rotavirus, porcine pararotavirus, or reovirus but was antigenically related to a bovine RVLV.

Purification and characterization of bovine rotavirus cores

Using the chaotropic effect generated by a high concentration of CaCl2, we converted calf rotavirus particles into cores of 40 nm in diameter. These cores were purified by rate zonal centrifugation in sucrose gradients and by isopycnic gradients. They had a sedimentation coefficient of 280S +/- 20S and a density of 1.44 g/ml in CsCl. When analyzed by polyacrylamide gel electrophoresis, they contained three polypeptides (VP125, VP89, and VP78). The major internal polypeptide of the virion (VP39) was recovered in a purified and soluble form in the top fractions of the sucrose gradients. From this stepwise degradation, it appears that VP39 is the most external polypeptide of dense particles. In contrast to reovirus cores, calf rotavirus cores did not exhibit transcriptase activity. Purified VP39 also did not exhibit transcriptase activity when tested after being mixed with purified rotavirus genome RNA as a template. Transcriptase activity was partially recovered when ionic conditions were adjusted to permit the reassociation of VP39 with the cores.

Characterization of an antigenically distinct porcine rotavirus

A porcine virus with rotavirus morphology, which was antigenically unrelated to previously described rotaviruses, is described. Particles with an outer capsid layer measured 75 nm and those lacking the outer layer were 63 nm in diameter. Particles which resembled cores were also identified. The virus was shown to be antigenically distinct from other rotaviruses as judged by immunofluorescence and immune electron microscopy, and it failed to protect piglets from challenge with porcine rotavirus. Analysis of the genome indicated that it was composed of 11 segments of double-stranded RNA with the same overall size range as other rotaviruses but with an unusual segment pattern.

Diagnostic virology using electron microscopic techniques

This chapter illustrates the development of the use of electron microscopy in viral diagnosis. The field covered is confined to medical viral diagnosis, but parallel developments have taken place in both veterinary and botanical fields and techniques derived from both these sources are also included where relevant. It is reported that the scanning transmission mode of operation, which can induce image contrast changes electronically, may enhance studies with unstained sections and perhaps facilitate thin section immune electron microscopy (IEM). The application of negative stain IEM has been particularly useful for the study of the antigenic nature of some of the newly discovered noncultivable viruses. Viral antigens can also be detected in thin sections of infected cells by IEM with suitably labeled specific antibodies. Confirmation of viral infection by electron microscopy on tissues originally processed for light microscopy is also frequently useful.

Thiocyanate and hydroxyl ions inactivate the scrapie agent

To probe the macromolecular structure of the scrapie agent and explore conditions for monomerization, the stability of the agent in low concentrations of inorganic ions was determined. A reduction by a factor of 10(5) in scrapie titer was found on exposure of the agent to 1 M KSCN or 0.3 M NaOH. In addition to the inactivation by thiocyanate ions, other chaotropic ions such as guanidinium and trichloroacetate inactivate the scrapie agent. Removal of thiocyanate ions by dialysis or glass permeation chromatography prevented the reduction in scrapie agent infectivity. Addition of equimolar amounts of (NH4)2SO4, a nonchaotrope, to preparations containing 1 M KSCN also prevented the loss of scrapie infectivity. In contrast, neutralization of the alkali-treated fractions with HCl did not restore infectivity. Acidification of partially purified fractions did not cause inactivation of the agent but did result in precipitation of the infectious agent. Inactivation by relatively low concentrations of chaotropic ions is consistent with many observations, all of which suggest that the scrapie agent contains a protein component that is essential for the maintenance of infectivity. Thus, it is unlikely that the agent is composed only of a "naked" nucleic acid. Certainly, if the agent were a naked nucleic acid, its lability in alkali virtually eliminates the possibility that it is composed of a single-stranded molecule of DNA.