Archives of Virology 66, 107--117 (1980) Archives of Virology O by Springer-Verlag 1980 Proteins Specified by African Swine Fever Virus I. Analysis of Viral Structural Proteins and Antigenic Properties By E. TABARI~S, M. A. MARCOTEGUI, M. FERNANDEZ, and C. SiNCHEz-BoTIJA Departamento de Virologfa Animal, Instituto Nacional de Investigaeiones Agrarias~ Madrid, Spain With 5 Figures Accepted April 29, 1980 Summary At least 28 polypeptides have been identified in intracellular virus, with molecular weights ranging from 11,500 to 243,000 daltons. By treatment with Nonidet P-40 and 2-mercaptoethanol it is possible to obtain subviral particles that have lost some proteins and have a density in CsC1 of 1.31 g/cm a which is higher than that of the complete virus (t.23 g/cma). _After addition of NaC1 the virus loses its major protein VP73 which indicates that it is localized in the viral envelope. Cores obtained after this treatment are made up of at least 14 proteins. Incorporation of 3H-fucose and 3H-glucosamine in intracellular virus occurs in three minor components. The protein VP42 is possibly the cell actin and appears to be strongly associated with the virus. It is not possible to eliminate it under conditions where the viral envelopes desappear morphologically. At least the proteins VPi72, VP162, VP146 and VP73 act as antigens in the natural infection. Introduction African swine fever virus (ASFV) is a DNA virus with icosahedral symmetry which is assembled in the cytoplasm (6, 11, 16) after synthesis of its DNA in the nucleus (20). ASFV is tentatively classified as an Iridovirus (2) and its natural hosts are the porcine species (12). The viral genome is linear, double stranded, infectious, with an approximate molecular weight of 10 s daltons (1, 8, 17). The number of structural proteins determined by polyacrylamide gel eleetrophoresis was found to vary in different laboratories (3, 18, 22). This paper deals with further progress made in the studies on the viral structural polypeptides, their localization within the virion and their antigenic role in the induction of antibodies in the natural infection. 0304-S60S/S0/0066/0107/$ 02.20