Biophysical studies of infectious pancreatic necrosis virus

Abstract

The MW of infectious pancreatic necrosis virus (IPNV) was determined by analytical ultracentrifugation and dynamic light scattering. The sedimentation coefficient of the virus was 435S. The average value for MW is (55 .+-. 7) .times. 106. The virus genome consists of 2 segments of double-stranded RNA (MW, 2.5 .times. 106 and 2.3 .times. 106), which represents 8.7% of the virion mass. The capsid protein moiety of IPNV consists of 4 species of polypeptides, as determined by polyacrylamide gel electrophoresis. The number of molecules of each polypeptide in the virion was determined. There are 22 molecules of the internal polypeptide .alpha. (MW, 90,000), 544 molecules of the outer capsid polypeptide .beta. (MW, 57,000), and 550 and 122 molecules, respectively, of the internal polypeptides .gamma.1 (MW, 29,000) and .gamma.2 (MW, 27,000). IPNV top component contains only the .beta. polypeptide species, and its MW is 31 .times. 106. The hydrodynamic diameter and EM diameter (calculated by catalase crystal-calibrated EM) of IPNV was compared with those of reovirus and encephalomyocarditis virus. Due to the swelling of the outer capsid, reovirus particles were much larger when hydrated (96-nm diameter) than when dehydrated (76-nm diameter), having a large water content and low average density. IPNV particles are more rigid, having nearly the same average diameter under hydrous (64 nm) as under anhydrous conditions (59.3 nm). Encephalomyocarditis virus has a very low water content and does not shrink at all when prepared for EM.