Polypeptide Synthesis in Simian Virus 5-Infected Cells

Abstract

Polypeptide synthesis in 3 different [mammalian] cell types infected with simian virus 5 was examined using high-resolution polyacrylamide slab gel electrophoresis, and all of the known viral polypeptides were identified above the host cell background. The polypeptides were synthesized in infected cells in unequal proportions, which are approximately the same as they are found in virions, suggesting that their relative rates of synthesis are controlled. The nucleocapsid polypeptide (NP) was the first to be detected in infected cells, and by 12-14 h the other virion structural polypeptides were identified, except for the polypeptides comprising the smaller glycoprotein (F). However, a glycosylated precursor (FO) with a MW of 66,000 was found in each cell type, and pulse-chase experiments suggested that this precursor was cleaved to yield polypeptides F1 and F2. No other proteolytic processing was found. In addition to the structural polypeptides, the synthesis of 5 other polypeptides, designated I through V, was observed in simian virus 5-infected cells. One of these (V), with a MW of 24,000, was found in all cells examined and may be a nonstructural viral polypeptide. There are polypeptides present in uninfected cells that correspond in size to polypeptides I through IV, and similar polypeptides were also detected in increased amounts in cells infected with Sendai virus. These findings, and the fact that the synthesis of all 4 of these polypeptides is not increased in every cell type, suggest that they represent host polypeptides whose synthesis may be enhanced upon infection. When a high salt concentration was used to decrease host cell protein synthesis in infected cells, polypeptides IV and (to a lesser extent) I were synthesized in relatively greater amounts than other cellular polypeptides, as were the viral polypeptides. The possibility that these polypeptides may play some role in virus replication is discussed.