Virus-specific Proteins Produced in HeLa Cells Infected with Poliovirus: Characterization of Subunit-like Protein*

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Abstract
HeLa-S3 cells infected with poliovirus were labelled with C14-leucine, and cytoplasmic extracts were analyzed for poliovirus specific proteins by means of sucrose gradient sedimentation followed by immunological precipitation. At least 2 virus-specific proteins or particles (designated as 10S and 80S substances), which were distinct from the mature virus (150S) on sedimentation, were found to be produced in the infected cells. The 80S substance corresponded to the capsid-like empty shells lacking infectivity. Peptide analyses of the tryptic digests of 10S, 80S, and 150S proteins labelled with either C14-isoleucine or C14-valine revealed that the 10S protein is quite similar in its primary structure to the viral capsid, this suggesting that the 10S substance is (or is composed of) a subunit protein of viral capsid. In a Ouchterlony''s precipitin tests in agar, it was found that HeLa cells infected with poliovirus produced 3 different antigens; well known N- and H-antigens (corresponded to the mature virus and empty shell, respectively) and a new antigen (S-antigen) which was less sedimentable in the ultracentrifugation and resistant to heat-treatment. The S-antigen apparently corresponded to the 10S protein foudn in the isotope experiments.