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Identification of a new element for RNA replication within the internal ribosome entry site of poliovirus RNA
Abstract:
Several mutants of the Mahoney strain of poliovirus type 1 have been generated by introducing mutations into the stem-loop II (SLII) structure within the internal ribosomal entry site (IRES). Four of these mutants (SLII-1, -4, -5 and -6 mutants) have been characterized previously and are host-range mutants that replicate well in human HeLa cells but not in mouse cells. Two deletion mutants, SLII-2 and SLII-3, were non-viable, even in HeLa cells. It is now reported that SLII-2 was defective in genome RNA synthesis and viral protein synthesis, while SLII-3 was defective only in viral protein synthesis. These results indicate that the SLII region contains a cis-element for RNA replication as well as for IRES-dependent translation and that these two functions lie at the same sites within the SLII region. The host cellular factors that interacted with wild-type SLII and mutant SLII-2 and SLII-3 RNAs were different, suggesting that different host-factor binding regulates expression of mutant phenotypes.
Insights
Mutations in poliovirus type 1's internal ribosomal entry site (IRES) stem-loop II (SLII) affect both viral RNA replication and protein synthesis. Different host factors binding to SLII regulate these distinct mutant phenotypes.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- The internal ribosomal entry site (IRES) of poliovirus type 1 is crucial for viral replication.
- The stem-loop II (SLII) structure within the IRES is essential for viral functions.
- Previous studies generated host-range mutants affecting replication in different cell types.
Purpose of the Study:
- To investigate the role of the SLII region in poliovirus genome RNA synthesis and viral protein synthesis.
- To identify cis-elements within SLII responsible for RNA replication and IRES-dependent translation.
- To explore the interaction of host cellular factors with wild-type and mutant SLII structures.
Main Methods:
- Generation of poliovirus type 1 mutants with alterations in the SLII region.
- Characterization of viable and non-viable mutants (SLII-1, -4, -5, -6, SLII-2, SLII-3).
- Analysis of genome RNA synthesis and viral protein synthesis defects in mutants.
- Investigation of host cellular factor interactions with different SLII RNAs.
Main Results:
- Deletion mutant SLII-2 exhibited defects in both genome RNA synthesis and viral protein synthesis.
- Deletion mutant SLII-3 showed defects exclusively in viral protein synthesis.
- The SLII region contains a cis-element regulating both RNA replication and translation.
- Different host cellular factors interacted with wild-type SLII and mutant SLII RNAs (SLII-2, SLII-3).
Conclusions:
- The SLII region of poliovirus IRES harbors a cis-element critical for both RNA replication and IRES-dependent translation.
- These two functions (replication and translation) are localized to the same sites within the SLII region.
- Differential binding of host factors to SLII structures dictates the observed mutant phenotypes, highlighting their role in regulating viral expression.