Protein synthesis directed by encephalomyocarditis virus mRNA. III. Discrete polypeptides translated from a monocistronic messenger in vitro

RNA derived from encephalomyocarditis virus directs the synthesis of 12 discrete polypeptides in a cell-free system derived from Krebs II ascites tumor cells. The largest of these proteins has a molecular weight greater than 120,000 and accounts for about 40% of the information present in the viral genome. This protein also contains most of the tryptic peptides found in the viral capsid and is analagous to an encephalomyocarditis precursor protein synthesized in vivo. In contrast to the maturation-cleavage mechanism which reduces this large precursor into smaller, mature viral proteins in vivo, the high molecular weight protein does not undergo maturation-cleavage in the cell-free system. Detailed studies involving the pulse-chase technique and peptide analysis of the discrete in vitro products indicate that they arise from a common translational initiation site, but are terminated at several unique points on the viral mRNA.