Virus precipitate was resuspended in
20 ml of 0.03 M sodiumepotassium phosphate buffer, pH 7.0 containing
0.005 M sodium DIECA. Gradient centrifugation was performed
by mixing cesium chloride with virus suspension (2.8 g/
10 ml) and centrifuged at 350,000 g at 20 C for 24 h.