Purification and Properties of Poliovirus

Energy Requirements for Loss of Viral Infectivity

Outside the host, viruses will eventually lose their ability to infect cells due to conformational changes that occur to proteins on the viral capsid. In order to undergo a conformational change, these proteins require energy to activate the chemical reaction that leads to the conformational change. In this study, data from the literature is used to calculate the energy required for viral inactivation for a variety of different viruses by means of the Arrhenius equation. We find that some viruses (rhinovirus, poliovirus, human immunodeficiency virus, Alkhumra hemorrhagic fever virus, and hepatitis A virus) have high inactivation energies, indicative of breaking of a chemical double bond. We also find that several viruses (respiratory syncytial virus, poliovirus, and norovirus) have nonlinear Arrhenius plots, suggesting that there is more than a single pathway for inactivation of these viruses.

Search for a prion-specific nucleic acid

Diversity of prion strains was attributed to an elusive nucleic acid, yet a search spanning nearly two decades has failed to identify a prion-specific polynucleotide. In our search for a prion-specific nucleic acid, we analyzed nucleic acids in purified fractions from the brains of Syrian hamsters infected with Sc237 prions. Purification of Sc237 prions removed nucleic acids larger than 50 nucleotides as measured by return refocusing electrophoresis (RRGE). To determine the size of the largest polynucleotide present in purified fractions at an abundance of one molecule per infectious (ID50) unit, we measured prions present after inoculation. In order to account for the rapid clearance of prions after intracerebral inoculation, we determined the number of PrP(Sc) molecules and ID50 units of prions that were retained in brain. Factoring in clearance after inoculation, we estimate that the largest polynucleotide present in our purified fractions at one molecule per ID50 unit is approximately 25 nucleotides in length. In the same fractions, there were approximately 3,000 protease-resistant PrP(Sc) molecules per ID50 unit after accounting for clearance of PrP(Sc) following inoculation. We compared the resistance of Sc237 and 139H prions to inactivation by UV irradiation at 254 nm. Irradiation of homogenates and microsomes diminished prion infectivity by a factor of approximately 1,000 but did not alter the strain-specified properties of the Sc237 and 139H prions. The data reported here combined with the production of synthetic prions argue that the 25-mer polynucleotides found in purified prion preparations are likely to be host encoded and of variable sequence; additionally, these 25-mers are unlikely to be prion specific.

Detection and identification of vaccine-related polioviruses by the polymerase chain reaction

We have used the polymerase chain reaction (PCR) to obtain sensitive detection and identification of poliovirus RNA genomes. Primer pairs were designed to permit identification of each Sabin poliovaccine strain by the electrophoretic mobilities of the amplified DNA products (Sabin 1: 97 bp; Sabin 2: 71 bp; Sabin 3: 44 bp). The compositions of samples containing mixtures of vaccine strains could be readily determined by PCR. When the amplified products were visualized by ethidium bromide fluorescence, as few as 250 genomic copies in the original sample could be detected. When PCR was used in combination with strain-specific 32P-labeled oligonucleotide probes, the limit of detection was less than or equal to 2.5 poliovirus genomes, exceeding the sensitivity of poliovirus isolation in cell culture by at least 100-fold. PCR amplifications may be performed on virion RNAs extracted directly from clinical specimens, potentially eliminating the requirement for virus isolation in routine identifications while yielding reliable results within 8 h.

Novel proteinaceous infectious particles cause scrapie

After infection and a prolonged incubation period, the scrapie agent causes a degenerative disease of the central nervous system in sheep and goats. Six lines of evidence including sensitivity to proteases demonstrate that this agent contains a protein that is required for infectivity. Although the scrapie agent is irreversibly inactivated by alkali, five procedures with more specificity for modifying nucleic acids failed to cause inactivation. The agent shows heterogeneity with respect to size, apparently a result of its hydrophobicity; the smallest form may have a molecular weight of 50,000 or less. Because the novel properties of the scrapie agent distinguish it from viruses, plasmids, and viroids, a new term "prion" is proposed to denote a small proteinaceous infectious particle which is resistant to inactivation by most procedures that modify nucleic acids. Knowledge of the scrapie agent structure may have significance for understanding the causes of several degenerative diseases.

Concentration and purification of poliovirus by ultrafiltration and isopycnic centrifugation

A method is described by which poliovirus can be rapidly and simply concentrated by the use of a Diaflo XM-50 ultrafilter membrane. Freon-extracted ultrafilter concentrates banded in CsCl provided a 1,724-fold volumetric concentration of poliovirus. During concentration, trypsin-digested cellular material can pass through the ultrafilter membrane, thus providing a versatile means of degrading and eliminating extraneous contaminating proteins. The ultrafilter concentration system is compared with the CsCl cushion system of poliovirus concentration, and both systems are further compared by banding virus and virus capsid material in CsCl by use of isopycnic centrifugation.

Biophysical and biochemical studies on rhinovirus and poliovirus. II. Chemical and hydrodynamic analysis of the rhinovirion

Chemical analysis of rhinovirus 14 revealed a ribonucleic acid (RNA) content of 29.8% and a high adenylic acid content (35%). A partial specific volume of 0.682 cm(3)/g was obtained for the rhinovirion. Rhinovirus and poliovirus had identical sedimentation coefficients of 158S. A diffusion coefficient of 1.71 x 10(-7) cm(2)/sec was consistent with a hydrated diameter of 25 nm for the rhinovirion. The calculated molecular weights of the rhinovirion and its genome were 7.1 x 10(6) and 2.1 x 10(6) daltons, respectively. Sedimentation analysis of infectious RNA confirmed the similarity of the molecular size of the poliovirus and rhinovirus genomes.

Poliovirus crystals within the endoplasmic reticulum of endothelial and mononuclear cells in the monkey spinal cord

The lumbar motor columns of a cynomolgus monkey that had become tetraplegic after experimental infection with a highly virulent strain of type 3 poliovirus were examined by electron microscopy. Crystalline aggregates of poliovirus occurred within the endoplasmic reticulum of endothelial cells as well as of mononuclear inflammatory cells. This finding suggests that the endoplasmic reticulum might be much more involved in poliovirus multiplication than has been previously supposed.