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5' termini of poliovirus RNA: difference between virion and nonencapsidated 35S RNA
Abstract:
Poliovirus cytoplasmic, nonencapsidated 35S RNA yields approximately one pUp per molecule upon T2 RNase digestion, indicating that this RNA has the same 5' end as the polyribosome-associated viral RNA fraction. Double-stranded, replicative form RNA after the same treatment yielded approximately four pNp structures per molecule, 65% of which was pUp. In contrast, the 35S RNA from mature virions contained no detectable pNp, indicating that the 5' end of the virion RNA is different from that of the nonencapsidated RNA. None of the above molecules contained pppNp, ppNp, or GpppNp structures present in host mRNA. The virion RNA molecules, as we have shown previously for thenonencapsidated 35S viral RNA (Fernandez-Muñoz and Darnell, 1976), is not labeled with [methyl-3H]methionine.
Insights
Poliovirus RNA found in the cytoplasm differs at its 5' end from the RNA within the virus particle. This difference in poliovirus RNA structure impacts viral replication and assembly.
Area of Science:
- Virology
- Molecular Biology
- RNA Biochemistry
Background:
- Poliovirus RNA serves as both the genome and mRNA.
- Understanding the 5' end structure of viral RNA is crucial for deciphering replication and translation mechanisms.
- Host mRNA typically possesses a 5' cap structure (pppNp, ppNp, or GpppNp), absent in poliovirus RNA.
Purpose of the Study:
- To characterize and compare the 5' end structures of different poliovirus RNA forms.
- To investigate potential differences between cytoplasmic, nonencapsidated viral RNA and virion-associated RNA.
- To determine if poliovirus RNA possesses a 5' cap structure similar to host mRNA.
Main Methods:
- T2 RNase digestion of poliovirus RNA species (cytoplasmic 35S RNA, replicative form RNA, and virion RNA).
- Analysis of 5' terminal nucleotide products (pUp, pNp) generated after enzymatic digestion.
- Comparison of digestion products with known host mRNA 5' end structures (pppNp, ppNp, GpppNp).
Main Results:
- Cytoplasmic, nonencapsidated 35S poliovirus RNA yields predominantly pUp after T2 RNase digestion, similar to polyribosome-associated viral RNA.
- Double-stranded replicative form RNA yields a mixture of pNp structures, with pUp being a major component.
- 35S RNA isolated from mature poliovirus virions shows no detectable pNp, indicating a distinct 5' end compared to cytoplasmic RNA.
- None of the analyzed poliovirus RNA molecules exhibit the 5' cap structures (pppNp, ppNp, GpppNp) characteristic of host mRNA.
Conclusions:
- Poliovirus RNA undergoes structural modifications at its 5' end during the viral life cycle.
- The 5' end of nonencapsidated cytoplasmic poliovirus RNA differs from that of virion RNA, suggesting distinct functional roles or processing steps.
- Poliovirus RNA initiation and/or processing pathways do not involve the canonical 5' cap structure found in host mRNA.