Role of myristoylation of poliovirus capsid protein VP4 as determined by site-directed mutagenesis of its N-terminal sequence.

Mutations were introduced by oligonucleotide-directed mutagenesis into the cDNA of poliovirus type 1 (Mahoney) in the region coding for the first five amino acids (myristoylation signal) of the viral capsid protein precursor P1. The cDNAs were then transcribed in vitro and the properties of the transcripts carrying the mutations studied in vitro by translation in a reticulocyte lysate or in vivo upon transfection of primate cells. Mutation of amino acid residue number 5 (Ser5----Thr) did not affect the viral phenotype, whereas mutations of residues number 1 (Gly1----Arg), 2 (Ala2----Pro) or 5 (Ser5----Pro) prevented myristoylation of P1 and were lethal. However, delayed production of virus was occasionally observed as the result of reverse mutations, which were found to restore a functional myristoylation signal as well as a wild-type virus phenotype. Thus, the myristoylation signal of the poliovirus polyprotein can accommodate Ala, Ser, Thr or Leu residues at position 2 and Ser, Thr or Ala residues at position 5. Mutations that altered myristoylation of P1 and affected virus viability did not prevent replication of the viral RNA but severely impeded in vitro processing of P1. This suggests that myristoylation plays a role in poliovirus capsid protein assembly.