Studies on the synthesis of viral RNA-polymerase-template complexes in BHK 21 cells infected with Semliki Forest virus

Abstract

Two main types of virus-specific RNA sedimenting at about 42 and 26 S, respectively, on sucrose density gradients are synthesized in animal cells infected with Semliki Forest virus (SFV). Two and one-quarter hours after infection of BHK 21 cells with SFV only about 10% of the total amount of virus-specific RNA that accumulates during the 8-hr growth cycle of the virus have been synthesized. If at this time an inhibitor of protein synthesis, cycloheximide, is added to infected cells, both of these RNA species are synthesized during the viral growth cycle with the same time course and in amounts similar to those in untreated cultures. This result suggests that the RNA polymerase-template complexes present at 2.25 hr post infection (p.i.) are stable and synthesize all virus-specific 42 and 26 S RNA accumulating during the viral growth cycle. These polymerase-template complexes are synthesized between 45 min and 2.25 hr p.i. During multiplication of SFV in BHK 21 cells the amount of radioactivity incorporated from radioactively labeled amino acids into protein during a series of labeling intervals decreases, and the ratio of synthesis of virus-specific proteins to cellular proteins increases. Both of these effects are not expressed to a significant extent at 2.25 hr post infection (p.i.). Sodium dodecyl sulfate-polyacrylamide-gel electrophoretic (SDS-PAGE) analysis of the polypeptides synthesized in infected cultures shortly after removal of cycloheximide, which had been present from 2.25 – 6 hr p.i. shows that cycloheximide does not block the development of these changes in cellular protein synthesis. Some implications of these findings concerning the synthesis of virus-specific RNA and the interference of virus multiplication with cellular protein synthesis are discussed.