Metabolic requirements for the maturation of respiratory syncytial virus

The metabolic processes required for maturation of respiratory syncytial (RS) virus was determined by testing with metabolic inhibitors in HeLa cells that had been trypsinized 18 h p.i. Although > 90% of the virus synthesized by that time remained cell-associated, treatment with trypsin inactivated at least 90% of the cell-associated virus. The trypsinized cells, when re-plated in virus growth medium, immediately resumed virus synthesis and this continued exponentially for at least 10 h, during which as little as 1 to 2 p.f.u./cell of new infectious virus could be detected. Treatment of these cells with 6-azauridine revealed that no further synthesis of virus RNA is required for a full yield of infectious virus. Treatment with cycloheximide, 2-deoxy-D-glucose and cytochalasin B suggested that neither protein synthesis nor glycosylation is required for the first 1 to 2 h following the resumption of virus production, but both processes are required for a full yield. These results suggest that with RS virus, the maturation process itself does not require RNA or protein synthesis or glycosylation. Trypsin, in addition to inactivating accumulated virus, released non-infectious particular material. The polypeptides of this material were similar to those of the RS virion except for a deficiency in glycoproteins. The trypsin apparently cleaved the virus glycoproteins on cell surfaces, which resulted in the inactivation of cell-associated virus and the release of a glycoprotein-deficient particle from cell surfaces. The pool of virus glycoproteins is evidently the limiting factor in infectious virus production by cells trypsinized 18 h p.i. The non-glycosylated polypeptides of cell-associated virus are the same as those of free virus.