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Two initiation sites for translation of poliovirus RNA in vitro: comparison of LSc and Mahoney strains

Previous studies in our laboratory provided evidence that the initiation of translation by the Mahoney strain of poliovirus type 1 RNA in vitro occurs at two unique sites. This study shows that the LSc strain of poliovirus type 1, a multistep, temperature-sensitive mutant of the Mahoney strain, also utilizes two sites for the initiation of translation in vitro. Incorporation of formyl-[35S]methionine into the amino terminus of newly synthesized polypeptides revealed the production of two labeled tryptic peptides which are identical in size and electrophoretic mobility with those produced by Mahoney virus. The polypeptides containing amino-terminal label showed similar patterns on sodium dodecyl sulfate-acrylamide gels, although one of the LSc polypeptides had a slightly faster mobility. The relative proportion of initiation at each site varied with the magnesium concentration for both viruses, but the LSc strain favored initiation at one site more so than did the Mahoney strain.