5′-Terminal nucleotide sequences of polio virus polyribosomal RNA and virion RNA are identical

Abstract

POLIO virus is a positive strand virus; it has a mRNA of the same 5′ to 3′ polarity and size as its virion RNA (ref. 1). It also has a protein covalently linked to its 5′-terminal end forming a 5′-terminus of protein–pU–U–A–A–A–A–C–A–Gp (refs 2, 3). This contrasts with other viral RNAs that either have di- or triphosphate 5′-termini (negative strand RNAs)4–6 or m7G5′ppp5′N(m)p… termini (most positive strand RNAs)7,8. The 5′-linked protein on poliovirion RNA is also found on at least two-thirds and perhaps all of the nascent chains of the replicative intermediate isolated from infected cells3. This suggests that the protein is linked to the RNA at a very early stage of replication, perhaps as a primer during the initiation of RNA synthesis2,3. The 5′-terminus of polio virus polyribosomal RNA lacks the protein and instead terminates in pUp… (refs 9, 10). Thus, it is possible that the protein initially present on the newly synthesised RNA chains is cleaved from that fraction of the RNA molecules destined to become mRNA. To determine the nucleotide sequence relationship between the polio virus RNAs containing and lacking the protein, we have isolated and sequenced the 5′-terminus of polio-virus polyribosomal RNA. We show here that its nucleotide sequence is identical to that of the 5′-terminus of virion RNA.