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Paramyxovirus mRNA editing leads to G deletions as well as insertions
J P Jacques1, S Hausmann, D Kolakofsky
1Department of Genetics and Microbiology, University of Geneva School of Medicine, Switzerland.
Abstract:
Paramyxoviruses are thought to edit their P gene mRNAs co-transcriptionally, by a mechanism in which the polymerase stutters and reads the same template base more than once. Sendai virus (SeV) and bovine parainfluenza virus type 3 (bPIV3) are closely related viruses, but SeV edits its P gene mRNA with the insertion of a single G residue (at approximately 50% frequency) within the sequence 5' A6G3, whereas bPIV3 inserts 1 to approximately 6 Gs at roughly equal frequency within the sequence 5' A6G4. When SeV synthetic mini-genomes containing either SeV or bPIV3 P gene editing cassettes are expressed from cDNA in cells which are also transfected with the SeV NP, P and L genes, the virus-specific editing patterns were reproduced. Since the bPIV3 editing pattern was reproduced in a system that is otherwise completely SeV, this suggests that all the information for the virus-specific editing patterns is due to the RNA sequence itself. Unexpectedly, the length of the template C run was found to be critical, even though it varies from 3 to 7 nucleotides in length in different viruses. Expanding this template C run first led to attenuation of the insertion phenotype, and then to deletions rather than insertions. A stuttering or slippage model to account for these events has been further refined to include a pressure which displaces the nascent strand in a given direction once it has disengaged from the template, and the similarities of this model to those which account for readthrough of cellular RNA polymerase transcription blocks are discussed.
Insights
Paramyxoviruses edit their P gene mRNA through polymerase stuttering. Sequence analysis revealed that the RNA sequence itself dictates virus-specific editing patterns, with template C run length critically influencing insertions or deletions.
Area of Science:
- Virology
- Molecular Biology
- RNA Editing
Background:
- Paramyxoviruses are known to edit their P gene mRNAs co-transcriptionally.
- This editing process is believed to occur via a polymerase stuttering mechanism, where the polymerase repeatedly reads the same template base.
- Sendai virus (SeV) and bovine parainfluenza virus type 3 (bPIV3) exhibit distinct P gene mRNA editing patterns.
Purpose of the Study:
- To investigate the mechanism of co-transcriptional RNA editing in paramyxoviruses.
- To determine if the RNA sequence itself contains all the information for virus-specific editing patterns.
- To explore the role of template C run length in P gene mRNA editing.
Main Methods:
- Expression of SeV synthetic mini-genomes with SeV or bPIV3 P gene editing cassettes in cells.
- Co-transfection with SeV NP, P, and L genes.
- Analysis of virus-specific editing patterns.
Main Results:
- Virus-specific P gene mRNA editing patterns of SeV and bPIV3 were reproduced in a heterologous SeV system, indicating sequence-dependent editing.
- The length of the template C run was found to be critical for editing outcomes.
- Expanding the template C run led to attenuated insertions and subsequent deletions, rather than insertions.
Conclusions:
- The RNA sequence itself encodes the information dictating virus-specific P gene mRNA editing patterns in paramyxoviruses.
- A refined stuttering/slippage model, incorporating template C run length and displacement pressure, can explain observed editing events.
- Similarities exist between this model and mechanisms explaining readthrough of cellular RNA polymerase transcription blocks.