The nucleic acid content of equine abortion virus.

The researchers analyzed the nucleic acid content of the equine abortion virus using techniques like differential centrifugation, microscopic examination and sedimentation. They found that DNA, making up about 9.2% of the particle’s estimated dry weight, comprised the virus. Remarkably, the composition of viral DNA’s bases was different compared to the host cell DNA.

Analysis of the Equine Abortion Virus

The research began with the purification of the equine abortion virus from the plasma of infected golden Syrian hamsters. The purification process involved:

• Differential centrifugation – a method used to separate cellular components based on size, shape and density.
• Nuclease treatment – an enzymatic reaction that breaks down nucleic acids, leaving the research team with a preparation clear of nonviral elements.

The purified virus was then checked using electron microscopy, which revealed that the virus was free from nonviral elements. Further sedimentation in sucrose and potassium tartrate density gradients resulted in a single visible band.

Characterization of the Virus Particles

Further electron microscopic examination of this band showed that it consisted of virus particles only. When these particles were injected into hamsters, they indeed caused infection and subsequent death of the animals.
The researchers estimated the following properties of the viral particles:

• A sedimentation coefficient of approximately 2200 S.
• A hydrated density of 1.18.
• An average diameter of 167 mμ, as directly observed from shadowed preparations in the electron microscope. Though, the calculated average diameter was 148 mμ, done using sedimentation and density data.

DNA Content and Composition of the Virus

Counting the particles and making colorimetric determinations, researchers found an average of 4.17 × 10−10 μg of DNA per particle, accounting for about 9.2% of the estimated dry weight of the particle.

To analyze the DNA composition, viral preparations were hydrolyzed and processed in chromatograms, resulting in detection of the constitutive bases of DNA. They found a pairing pattern with adenine approximately equal to thymine and guanine to cytosine. They noted a significant difference in the molar dissymmetry ratio (A + T/G + C) between the viral DNA (0.78) and host cell DNA (1.40). This ratio describes the balance of the above-mentioned base pairs in the DNA sequence. The closer it is to 1, the more balanced is the DNA composition.