Covalent linkage of a protein to a defined nucleotide sequence at the 5'-terminus of virion and replicative intermediate RNAs of poliovirus.

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Abstract
The 5''-terminus of poliovirus polyribosomal RNA is pUp. A candidate for the 5''-terminus of poliovirion RNA was recovered as a compound migrating toward the cathode when 32P-labeled virion RNA was completely digested with RNase T1, T2 and A and analyzed by paper ionophoresis at pH 3.5. Treatment with proteinase K reversed its direction of migration, indicating the presence of protein. Treatment with venom phosphodiesterase liberated all of the radioactivity as pUp, suggesting that poliovirion RNA has a protein-pUp 5''-terminus. Treatment of virion RNA with T1 RNase alone generated a proteinase K-sensitive oligoribonucleotide. Analysis of the oligoribonucleotide using RNase A and U2 showed its structure to be protein-pU-U-A-A-A-A-C-A-G. Digests of replicative intermediate RNA contained sufficient protein-pUp to suggest that this structure is at the 5''-end of most nascent poliovirus RNA molecules. A protein-nucleotide structure probably acts as a primer for initiating synthesis of poliovirus RNA.