Myristoylation of the poliovirus polyprotein is required for proteolytic processing of the capsid and for viral infectivity.

The poliovirus polyprotein is cotranslationally linked to myristic acid at its amino-terminal glycine residue. We investigated the role of myristoylation in the viral replication cycle by site-directed mutagenesis of this glycine codon. Synthetic full-length RNA transcripts carrying a Gly-to-Ala mutation (G4002A) gave no infectious virus on transfection into permissive cells (HeLa). However, mutant viral RNA was replicated in the transfected cells, albeit at a reduced level. The virus-specific polypeptide P1, the precursor for the capsid proteins, was found in HeLa cells transfected with wild-type or mutant RNA, but only the wild-type P1 was myristoylated; the G4002A mutant P1 was not myristoylated. We also introduced the G4002A mutation into an in vitro transcription-translation vector encoding poliovirus P1 precursor. Processing of the mutant precursor by poliovirus-infected cell lysate (providing 3Cpro and 3CDpro activities) was severely inhibited, whereas the normally inefficient cleavage by purified 3Cpro was not affected. These results suggest that the myristic acid moiety of the P1 precursor may be required for efficient processing by 3CDpro.