Abstract
Newcastle disease virus (Herts strain), grown in embryonated eggs or in a line of bovine kidney cells, was purified and then separated by sucrose density gradient centrifugation into infectious (IH) and noninfectious hemagglutinating (NIH) particles. These particles were morphologically similar, although the average size of IH was twice that of NIH particles. The activity of hemagglutinin per milligram of virus protein was two- to threefold higher in NIH particles than in IH particles, whereas the specific activity of neuraminidase did not differ in the two particle types. This was consistent with the observed particle size difference. The distribution of the major proteins in IH and NIH particles from egg-grown virus, determined by polyacrylamide gel electrophoresis (PAGE), was significantly different. In IH particles the molar ratio of protein 1 (74,000 daltons) to proteins 2 and 3 (56,000 daltons): protein 6 (41,000 daltons) was 1.0:2.5:2.5; in NIH particles the ratio was 1.0:0.6:1.0. When Newcastle disease virus was grown in bovine kidney cells, the molar ratio of proteins in IH particles resembled that of of egg-grown virus. However, in NIH particles from bovine kidney cells, only protein bands corresponding to protein 1 and proteins 2-3 were present and their molar ratio was 1.0:0.6. Protein 6 was marginally detectable in these particles. Analysis of the proteins in [3H]isoleucine- and [14C]glucosamine-labeled virus showed proteins 1 and 2 (glycoproteins) present in the ratio of 1.0:0.5; protein 3, the nucleoprotein, was not detected. These results are compatible with previous findings by others that NIH particles are deficient in RNA and nucleoprotein antigen, and suggest that formation of discrete particles of Newcastle disease virus by budding requires at most minimal amounts of proteins 3 or 6. The fatty acid composition of egg-grown IH and NIH particles was not significantly different and resembled that of normal allantoic fluid.