Ribonucleic acid of foot-and-mouth disease virus: Its preparation, stability, and plating efficiency on bovine-kidney cultures

Abstract

Infectious ribonucleic acid (RNA) from foot-and-mouth disease virus, type A, was examined as to its method of preparation, stability, and plating efficiency on calf-kidney cultures. The best yields of RNA were obtained with cold phenol at low ionic strength in the presence of EDTA and sodium dodecylsulfate. One extraction with phenol was sufficient to destroy all ribonuclease (RNAase)-resistant virus particles and gave the maximum yields of RNA. The isolated RNA was completely stable to storage at −196°C but not at 4°, −12° and −50°C. It was more stable than the virus itself to acid and alkaline conditions from pH 3.0 to 11.5. When acidified to pH 4.1 in the absence of RNAase, the virus did not appear to split off infectious RNA. There was a linear relationship between plaque counts in tissue culture and the dilution of RNA applied, and replicate platings produced a Poissonian distribution of plaque counts. The plating of RNA was considerably more efficient when small-sized (i.e., 0.1 ml) inocula were used than when the same amount of RNA was applied in larger volumes. Under such conditions the infection of culture cells appeared to be rapid, i.e., as many plaques were formed when the agar overlay was applied 1 minute after plating RNA as when applied at later times.