Quantitative study of the formation of poliovirus antigens in infected HeLa cells

Picornavirus morphogenesis

The Picornaviridae represent a large family of small plus-strand RNA viruses that cause a bewildering array of important human and animal diseases. Morphogenesis is the least-understood step in the life cycle of these viruses, and this process is difficult to study because encapsidation is tightly coupled to genome translation and RNA replication. Although the basic steps of assembly have been known for some time, very few details are available about the mechanism and factors that regulate this process. Most of the information available has been derived from studies of enteroviruses, in particular poliovirus, where recent evidence has shown that, surprisingly, the specificity of encapsidation is governed by a viral protein-protein interaction that does not involve an RNA packaging signal. In this review, we make an attempt to summarize what is currently known about the following topics: (i) encapsidation intermediates, (ii) the specificity of encapsidation (iii), viral and cellular factors that are required for encapsidation, (iv) inhibitors of encapsidation, and (v) a model of enterovirus encapsidation. Finally, we compare some features of picornavirus morphogenesis with those of other plus-strand RNA viruses.

Composition of artificially produced and naturally occurring empty capsids of poliovirus type 1

The polypeptide composition of the empty capsids of poliovirus type 1 represented either by the 73 S component isolated from sucrose gradients or by the top component from CsCl gradients is different from that ot the whole infectious virion. One protein (VP4) is absent from the empty capsids, another (VP2) is lower in relative amount, while an additional protein (NCVP6), not present in purified virions, is found in large amounts. Artificial production of 73 S particles by borate buffer, pH 10.5, treatment of purified virions results in removal of one protein component (VP4) and the RNA of the virus. The observed differences in composition of these virus-specific particles are discussed with regard to their possible role in the architecture and the assembly of the virion.

Picornavirus inhibitors

Picornaviruses are among the best understood animal viruses in molecular terms. A number of important human and animal pathogens are members of the Picornaviridae family. The genome organization, the different steps of picornavirus growth and numerous compounds that have been reported as inhibitors of picornavirus functions are reviewed. The picornavirus particles and several agents that interact with them have been solved at atomic resolution, leading to computer-assisted drug design. Picornavirus inhibitors are useful in aiding a better understanding of picornavirus biology. In addition, some of them are promising therapeutic agents. Clinical efficacy of agents that bind to picornavirus particles has already been demonstrated.

Binding of neutralizing monoclonal antibodies to empty capsids of poliovirus can be blocked by monospecific antisera to structural polypeptides VP1 and VP2

Binding of two neutralizing monoclonal antibodies (Nt-mAbs) to natural empty capsids (NEC) of poliovirus, type 1, was blocked to the extent of 83 per cent to 98 per cent by monospecific rabbit antisera directed against the structural polypeptides VP1 and VP2. Monospecific antisera against VP3 or VP4, however, did not show this blocking effect. It is therefore assumed that VP1 and VP2 are located close together at the antigenic sites for the two mAbs.

Poliovirus morphogenesis. I. Identification of 80S dissociable particles and evidence for the artifactual production of procapsids

The current model of poliovirus morphogenesis postulates a fundamental role for procapsid, 80S shells that, upon interaction with viral RNA and subsequent proteolytic cleavage, give rise to complete virus particles. Although 80S sedimenting particles can, indeed, be isolated from cytoplasmic extracts of infected cells, their physical properties differ from those reported for procapsids. Far from being stable structures, they can be dissociated by pH 8.5 and 0.1% sodium dodecyl sulfate into slower-sedimenting subunits. The reasons for this discrepancy were investigated, and two main modalities leading to the appearance of procapsids in vitro were identified. The first involves a temperature-mediated conversion of dissociable 80S particles into stable 80S procapsids, and the second involves the self-assembly of endogenous 14S subunits, also primed by an increase in the temperature of cytoplasmic extracts.

Density of infectious virus and complement-fixing antigens of two rhinovirus strains

Dans, P. E. (National Institute of Allergy and Infectious Diseases, Bethesda, Md.), B. R. Forsyth, and R. M. Chanock. Density of infectious virus and complement-fixing antigens of two rhinovirus strains. J. Bacteriol. 91:1605-1611. 1966.-Two rhinovirus serotypes (echovirus 28 and HGP) and poliovirus type 1 were banded by isopycnic centrifugation in cesium chloride. The rhinovirus virions had a density of 1.41 g/ml, whereas that of poliovirus was 1.34. Since a number of other enteroviruses also have a density of 1.34 g/ml in cesium chloride, a basic difference in density may exist between the rhinovirus and enterovirus subgroups of the picornavirus family. Whether this difference reflects differences in ribonucleic acid content or binding of cesium ions remains to be determined. In tests with echovirus 28 two peaks of CF activity were detected: one in association with the virion (1.41 g/ml), and a larger peak of lower density (1.30 g/ml). With echovirus 28 antiserum, a heterotypically reactive complement-fixing (CF) antigen was detected in the HGP virus suspension at a density less than that of the virion (1.30 g/ml). This antigen corresponded in density to the less dense CF antigen of echovirus 28.

KINETICS OF SYNTHESIS OF VARIOUS TYPES OF ANTIGENIC PROTEINS IN CELLS INFECTED WITH PSEUDORABIES VIRUS

Hamada, Chuya (Albert Einstein Medical Center, Philadelphia, Pa.), and Albert S. Kaplan. Kinetics of synthesis of various types of antigenic proteins in cells infected with pseudorabies virus. J. Bacteriol. 89:1328-1334. 1965.-By means of an indirect precipitation test, a determination was made of the rates of synthesis of various types of serologically specific proteins in rabbit kidney cells infected with pseudorabies virus. The rate of synthesis of cell-specific protein decreased after infection. During the early stages of the infective process, proteins which bear no precursor relationship to the viral particles (nonstructural viral proteins) and which cannot be detected in noninfected cells were formed. Almost concurrently with these nonstructural proteins, synthesis of virus precursor proteins began. The synthesis of these proteins preceded the formation of mature virus and continued until the end of the virus growth cycle.