Infectious bovine rhinotracheitis (IBR) virus was purified by rate zonal and isopycnic centrifugation in potassium tartrate gradients. Viral nucleocapsids were isolated from purified virions by treatment with the nonionic detergent Triton X-100 followed by high speed centrifugation. This treatment was shown to produce a suspension of 74% completely de-enveloped nucleocapsids, 24% incompletely de-enveloped nucleocapsids, and 2% whole virions. The viral nucleocapsids contained DNA and banded at a density of 1.25 g/cm3. Analysis of the viral polypeptides by gradient SDS-polyacrylamide gel electrophoresis revealed that 33 virion proteins, ranging in molecular weight from 13,000 to 275,000 dalton, were present in the complete virus particle. Detergent treatment of the virus quantitatively removed two of the major proteins (vp8, 90,000 dalton, and vp13, 73,000 dalton) and partially removed eleven other proteins. Fifteen viral polypeptides appeared to remain firmly associated with the viral nucleocapsids.
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