| Abstract: | The origin of the envelope lipids acquired by Rous sarcoma virus (RSV) and vesicular stomatitis virus (VSV) during budding from the plasma membrane of chicken embryo fibroblasts was examined. Several differences were observed between the lipid composition of RSV and the plasma membrane. When the phospholipid composition of the cells was modified by growing them in the presence of the choline analogues, N,N-dimethylethanolamine or l-2-amino-1-butanol, the phospholipid composition of the virus was subsequently altered but in a very different manner than the plasma membrane. In the plasma membrane, the increase in the analogue-containing phospholipid was at the expense of phosphatidylcholine and phosphatidylethanolamine while the amount of sphingomyelin remained constant. In RSV, however, there was a decrease in sphingomyelin and phosphatidylethanolamine while there was only a small change in the amount of phosphatidylcholine. Phospholipid polar head group modification did not significantly alter the fatty acid composition or the cholesterol content. Membranes of phagosomes isolated after the cells had ingested latex beads had essentially the same phospholipid composition as the plasma membrane. The phospholipid composition of VSV was different from RSV, but it also did not reflect the composition of the plasma membrane. The composition of the plasma membrane was intermediate between the viruses and the endoplasmic reticulum, but contamination of the plasma membrane fraction with the endoplasmic reticulum could not account for the observed differences. These results show that the viruses bud from localized lipid regions that do not reflect the average properties of the plasma membrane. |
