Polypeptides and structure of African swine fever virus

Extracellular and intracellular African swine fever virus (ASFV) was purified using a two-phase aqueous polymer system. Both the structure of the virus and the polypeptides present during the purification procedure were studied. After PEG/dextran phase separation and centrifugation through 20% (w/v) Ficoll, 79% of input infectivity was recovered as semi-purified virus. The density of the virus after equilibrium centrifugation in sucrose was 1.19 g/ml. The envelope of the virion consisting of a unit membrane was removed from the virion after centrifugation in sucrose. Removal of envelope was associated with the loss of a 230 kilodalton (kd) glycoprotein from the virion. Disruption of the viral surface structure resulted in a loss of infectivity. Eighteen of the most prominent of the 33 polypeptides of extracellular or cell free (CF) virus were those with molecular weights of 230, 195, 165, 155, 150, 125, 116, 97, 92, 73, 62, 58, 50, 45, 35, 33, 25 and 11 kd, while the fourteen most prominent polypeptides in intracellular or cell associated (CA) virus were 103, 97, 92, 84, 73, 62, 58, 54, 47, 45, 35, 33, 25 and 17 kd. The 45 kd polypeptide may be actin which copurifies with the virus. No major differences were found in the number or size of proteins among three isolates of ASFV. Electron micrographs of thin sections of ASFV show the capsid to consist of a distinct double layer of closely packed capsomeres enclosed on both sides with a semi-transparent layer. Cell associated virus measured from side-to-side 188 nm and vertex-to-vertex 212 nm. The capsid encloses an inner core composed of a dense nucleoid surrounded by a 40-48 nm layer of core protein.