Cleavage of poliovirus-specific polypeptide aggregates.

Zonal electrophoresis resolves two aggregates of poliovirus type 2 cytoplasmic polypeptides. The more negatively charged aggregate contains mainly noncapsid viral-specific polypeptides (NCVP) 2 and x, whereas the other consists of the capsid polypeptides (VP) 0, 1, 2, and 3 (VP0, VP1, VP2, VP3). After treatment with sodium deoxycholate (DOC), the aggregates sediment at 5 to 6S. Their electrophoretic mobilities are unaffected by DOC or RNase. The capsid polypeptide aggregate is similar in mobility to virions but can be converted to a faster electrophoretic form, resembling empty capsids, by heating. If infected HeLa cells are allowed to synthesize poliovirus polypeptides in the presence of iodoacetamide, no capsid polypeptides are produced, but rather NCVP1a (the precursor to capsid polypeptides) is accumulated, along with NCVP2 and NCVPx. When analyzed by electrophoresis and centrifugation, uncleaved NCVP1a migrates with the NCVP2-x aggregate. NCVP1a can be cleaved to capsid-like polypeptides in vitro by using extracts of infected cells, but not uninfected cells, indicating either a virus-specified protease or a cellular enzyme activated during infection. After cleavage of NCVP1a by infected cell extracts, the capsid polypeptides which are produced dissociate from the NCVP2-x complex.