Complete translation of poliovirus RNA in a eukaryotic cell-free system.

Poliovirus RNA stimulates imcorporation of 35S from both [35S]methionine and formyl-[35S]methionyl-tRNAfMet in cell-free systems derived from HeLa cells or from poliovirus-infected HeLa cells. The largest product formed under the direction of the viral RNA is the same size as the polyprotein thought to represent translation of the entire RNA. Synthesis of this polyprotein and other large products was stimulated greatly by increasing the salt concentration during the reaction from the optimum for initiation (90 mM) to the optimum for elongation (155 mM). Only one initiation peptide could be identified, and a tryptic digest of the product contained mainly peptides that cochromatographed with peptides from authentic viral proteins. The RNA from a deletion mutant of poliovirus initiated protein synthesis at the same site used by standard RNA and programmed synthesis of an appropriately deleted set of polypeptides. The results strongly support the model of translation of poliovirus RNA from a single initiation site into a continuous polyprotein that is cleaved to form the functional proteins. It is suggested that uninfected HeLa cell extracts can carry out the cleavages of nascent polyprotein.