Poliovirus superinfection of Sendai virus-infected cells inhibited the syntheses of the structural P protein and the nonstructural C' and C proteins equally. As the Sendai virus P, C', and C proteins are all translated from the same mRNA by ribosomes which initiate on alternate AUGs and as non-poliovirus protein synthesis is inhibited in poliovirus-infected cells by inactivation of initiation factors responsible for cap group recognition, these results indicate that cap group recognition is important for ribosome initiation on AUGs which are not proximal to the 5' end of the mRNA.