A comparison has been made of some of the serological and physicochemical properties of a virulent and an avirulent strain of foot-and-mouth disease virus, serotype SAT. The avirulent strain (SAT-82) was derived from the virulent strain (SAT-7) by serial passage in BHK 21 cells. The viruses were indistinguishable in cross-neutralization tests. In immunodiffusion tests a clear spur line was obtained with the SAT-82 antiserum but not with SAT-7 antiserum. The major polypeptides of the two viruses were identical when examined by polyacrylamide gel electrophoresis.

Hybridization and thermal denaturation experiments failed to distinguish between the RNAs but two-dimensional electrophoresis of the oligonucleotides produced by ribonuclease T digestion revealed several differences. Possibly the most significant of these differences was the size of the polycytidylic acid [poly (C)] tract. There were about 170 nucleotides in the poly (C) tract of the SAT-7 RNA compared with around 100 in the SAT-82 RNA. Further evidence for this deletion was provided by the slightly different behaviour of the two RNAs when compared by sucrose gradient centrifugation and polyacrylamide gel electrophoresis.


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