Infectious double-stranded poliovirus RNA

A structural model for the genome of echovirus 22

We have proposed previously that the structural model for the echovirus 22 genome is a single-stranded RNA molecule that has folded back upon itself to form a stable "hairpin" at the 5'-terminus. The vRNA of echovirus 22 has been characterized further by digestion with selective ribonucleases, electrophoresis in composite gels, hydrodynamic studies in density gradients of Cs2SO4 and sucrose, thermal denaturation and 3'-terminal ribonucleotide analysis. Based on these observations, the genome of echovirus 22 is a single-stranded RNA molecule having a region of secondary structure located at the 5'-terminus that may be characterized as a snapback hairpin with hydrogen-bonded base-pairing. In addition, a VPg-like protein is attached (presumably to the 5'-end of the RNA) and the 3'-terminus contains a polyadenylic acid tract [poly (A)].

In vitro RNA synthesis by viruses isolated from the yeast Yarrowia lipolytica

Viruses isolated from the yeast Yarrowia lipolytica possess a DNA-independent RNA polymerase activity which is inhibited by ethidium bromide and by sodium pyrophosphate but not by actinomycin D. RNA synthesis is maximum at pH 8.0 and at 30 degrees C. Newly synthesized RNA molecules are largely released from the particles, are single-stranded and are able to hybridize with denatured viral genomic RNA.

Evidence for secondary structure within the virion RNA of echovirus 22

Phenol-extracted echovirus 22 virion RNA is infectious, but unlike poliovirus virion RNA, it resists digestion with pancreatic RNase and nuclease P-1, a 3' exonuclease selective for single-stranded RNA. These data indicate the presence of an enzyme-resistant portion somewhere in the RNA molecule and suggest that it is a double-stranded or base-paired region distant from the unblocked 3' terminus. Equilibrium density gradient centrifugation of native echovirus 22 virion RNA results in a single peak with a density of 1.63 g/cm3. When sheared before centrifugation, the molecule is resolved into two RNA species: one with an approximate density of 1.70 to 1.71 g/cm3, as is observed also for single-stranded poliovirus virion RNA, and the other with a density of 1.58 to 1.59 g/cm3. Data obtained from rate zonal centrifugation may be used to calculate an approximate sedimentation coefficient corrected to water at 20 degrees C of 34 and a molecular weight of 2.4 X 10(6) for the virion RNA. We propose a model for echovirus 22 RNA composed of a linear RNA molecule with a 5' hairpin.

The structure of poliovirus replicative form

The structure of polio replicative form (RF) has been investigated by 3' end labeling and the use of polynucleotide phosphorylase to now allow a complete composite of the RF structure. The evidence presented indicates that the 3' terminal sequence of the minus strand is an exact complement to the 5' end of polio RNA. This suggests that the 5' terminal U of polio RNA is genetically coded. Other data is presented to show that in addition to the genetically coded poly(A) tract of the plus strand in RF, a single-stranded poly(A) tail protrudes beyond the double-stranded RNA.

Synthesis of ribonucleic acid in cells infected with LSc poliovirus at elevated temperatures

The synthesis of viral ribonucleic acid (RNA) was detected within 2 hr after infection with LSc poliovirus at 35 C. This RNA eluted as a single peak with 0.9 m NaCl on methylated albumin celite columns, was sensitive to ribonuclease, precipitated in the presence of 2 m LiCl, and had an S(20) value at 34 +/- 2 in linear sucrose gradients. When cells were infected at 39 to 40 C, there was also early synthesis of RNA. However, 2 hr after infection this synthesis was drastically inhibited. The absence of net RNA synthesis at 39 to 40 C during the late stages of infection was not caused by rapid degradation of newly formed RNA, since the RNA produced between 1 and 2 hr at 39 to 40 C was still present 3.5 hr after infection. There was a 3 log(10) inhibition in the production of infectious virus when p-fluorophenylalanine was present in the medium at a concentration of 25 mug/ml. This concentration of analogue had little effect upon the production of viral polymerase and viral RNA. Virus grown in the presence of analogue at a concentration of 10 mug/ml exhibited increased heat sensitivity compared to control virus. However, viral polymerase exhibited no change in sensitivity to heat or manganese when cells were exposed to 25 mug of p-fluorophenylalanine per ml during infection. p-Fluorophenylalanine had a relatively selective effect on viral capsid protein but did not reverse the inhibition of synthesis of viral RNA at 39 to 40 C.

Characterization of influenza virus ribonucleic acid duplex produced by annealing in vitro

A ribonuclease-resistant ribonucleic acid (RNA) with a sedimentation coefficient of 12S was obtained by self-annealing influenza virus-specific RNA isolated from infected cells. It had the properties of double-stranded RNA. (i) Sedimentation behavior in sucrose gradient was independent of salt concentration. (ii) Thermal transition profile was sharp; the melting temperature is 83 C in 0.1 SSC (0.15 m NaCl plus 0.015 m sodium citrate) and 98 C in SSC. (iii) Buoyant density in cesium sulfate was 1.58 g/cm(3) compared to 1.64 g/cm(3) for single-stranded RNA. (iv) It gave rise to single-stranded RNA after denaturation. (v) The 12S RNA duplex contained both plus and minus strands of influenza virus. Labeled plus strands could be displaced by extraneous cold plus strands and extraneous (32)P-labeled plus strands could be incorporated into duplex after denaturation and reannealing.

Synthesis of reovirus ribonucleic acid in L cells

Kudo, Hajime (The Wistar Institute of Anatomy and Biology, Philadelphia, Pa.), and A. F. Graham. Synthesis of reovirus ribonucleic acid in L cells. J. Bacteriol. 90:936-945. 1965.-There is no inhibition of protein or deoxyribonucleic acid (DNA) synthesis in L cells infected with reovirus until the time that new virus starts to form about 8 hr after infection. At this time, both protein synthesis and DNA synthesis commence to be inhibited. Neither the synthesis of ribosomal ribonucleic acid (RNA) nor that of the rapidly labeled RNA of the cell nucleus is inhibited before 10 hr after infection. Actinomycin at a concentration of 0.5 mug/ml does not inhibit the formation of reovirus, although higher concentrations of the antibiotic do so. Pulse-labeling experiments with uridine-C(14) carried out in the presence of 0.5 mug/ml of actinomycin show that, at 6 to 8 hr after infection, two species of virus-specific RNA begin to form and increase in quantity as time goes on. One species is sensitive to ribonuclease action and the other is very resistant. The latter RNA is probably double-stranded viral progeny RNA, and it constitutes approximately 40% of the RNA formed up to 16 hr after infection. The function of the ribonuclease-sensitive RNA is not yet known. Synthesis of both species of RNA is inhibited by 5 mug/ml of actinomycin added at early times after infection. Added 6 to 8 hr after infection, when virus-specific RNA has already commenced to form, 5 mug/ml of actinomycin no longer inhibit the formation of either species of RNA.