Regulation of protein synthesis in HEp-2 cells and their cytoplasmic extracts after poliovirus infection

Abstract

In intact HEp-2 cells, the overall rate of protein synthesis decreased rapidly after poliovirus infection. Under the controlled energetic and ionic in vitro assay conditions, however, cytoplasmic extracts prepared late in infection exhibited an increased translational activity. This resulted from multiple reinitiation cycles of poliovirus RNA translation. Increased ion concentrations in the in vitro translation reaction mixtures inhibited both the rate of peptide chain initiation and elongation for cellular mRNA translation. However, excess salts inhibited the rate of polypeptide chain elongation for poliovirus in vitro translation to a higher extent than the rate of initiation. A virus-induced shut off of host cell protein synthesis was observed in vivo as well as in the in vitro translation system. Translation of cellular mRNAs in cytoplasmic extracts prepared late in infection was restored by addition of uninfected cell extract free of endogenous mRNA. We concluded that increased concentrations of ions in poliovirus-infected cells account for the decrease in the overall rate of protein synthesis, but are not involved in the mechanism of poliovirus-induced shut off of host cell protein synthesis.