A factor that restores translation of capped mRNAs in poliovirus-infected HeLa cell extracts was purified and identified as the 24,000-dalton cap-binding protein.
The study identifies the restoring factor for translation in poliovirus-infected cells as the cap-binding protein, suggesting poliovirus inactivates this protein to inhibit cellular protein synthesis.
It was previously shown that the poliovirus-induced inhibition of translation of capped mRNAs can be reversed by a protein found in preparations of the eukaryotic initiation factor eIF-4B Rose, J. K., Trachsel, H., Leong, K. & Baltimore, D. (1978) Proc. Natl. Acad. Sci. USA 75, 2732--2736. This "restoring factor" has now been purified from a high-salt wash of rabbit reticulocyte ribosomes by taking advantage of its tight association with factor eIF-3 at low salt concentrations. It did not copurify with the major Mr 80,000 polypeptide of eIF-4B preparations but did copurify with a Mr 24,000 polypeptide previously shown to bind to the cap structures of mRNAs Sonenberg, N., Rupprecht, K. M., Hecht, S. M. & Shatkin, A. J. (1979) Proc. Natl. Acad. Sci. USA 76, 4345--4349. Both the electrophoretic mobility and the tryptic peptide pattern of the restoring factor were indistinguishable from those of the cap-binding protein, and the restoring factor could be crosslinked to the 5'-terminal cap on mRNA. Thus, is appears that poliovirus inhibits cellular protein synthesis by inactivation of some crucial property of the cap-binding protein.
Trachsel et al. (1980) studied Poliovirus infection (in vitro model). Purified restoring factor (cap-binding protein) was evaluated on Restoration of VSV mRNA translation in extracts from poliovirus-infected HeLa cells. A factor that restores translation of capped mRNAs in poliovirus-infected HeLa cell extracts was purified and identified as the 24,000-dalton cap-binding protein.