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Regulation of polyoma virus transcription in murine embryonal carcinoma cells
Abstract:
Undifferentiated murine embryonal carcinoma (EC) cells are resistant to infection with wild-type polyoma virus. The block appears to be located at the transcriptional level. Polyoma host range mutants capable of expressing early and late functions in EC cells have been isolated. The modifications responsible for the phenotype of these mutants are localized in the noncoding region of polyoma DNA genome, containing regulatory sequences for replication and transcription. We compared the 5' termini of early and late mRNAs of wild-type polyoma and mutant viruses in EC cells and in permissive cells. Our results show that wild-type mRNA is normally spliced in EC cells but present at a very low level. The sequence modifications of the mutant viruses lead to a 100-fold increase in the production of mRNA in these cells, but the major 5' termini of early and late mRNAs are identical to those in wild-type-infected 3T6 cells.
Insights
Murine embryonal carcinoma (EC) cells resist wild-type polyoma virus infection due to transcriptional blocks. Host range mutants overcome this resistance by altering noncoding DNA regions, significantly increasing viral mRNA production in EC cells.
Area of Science:
- Virology
- Molecular Biology
- Cancer Research
Background:
- Undifferentiated murine embryonal carcinoma (EC) cells exhibit resistance to wild-type polyoma virus infection.
- This resistance is primarily attributed to a block at the transcriptional level.
Purpose of the Study:
- To investigate the molecular mechanisms underlying polyoma virus infection resistance in EC cells.
- To identify genetic modifications in polyoma virus that enable infection and gene expression in EC cells.
Main Methods:
- Isolation and characterization of polyoma host range mutants capable of growth in EC cells.
- Comparison of 5' termini of early and late messenger RNAs (mRNAs) between wild-type and mutant viruses in EC and permissive cells.
- Analysis of regulatory sequences within the polyoma DNA genome.
Main Results:
- Polyoma host range mutants were identified, with modifications localized in the noncoding DNA region.
- These modifications enhance viral gene expression, leading to a 100-fold increase in mRNA production in EC cells.
- Despite increased production, the 5' termini of mutant and wild-type mRNAs in EC cells are similar to those in permissive cells, indicating normal splicing.
Conclusions:
- The noncoding region of polyoma DNA contains critical regulatory elements for replication and transcription in EC cells.
- Mutations in this region can overcome the transcriptional block, enabling productive viral infection in resistant EC cells.
- Viral mRNA splicing is functional in EC cells, but wild-type virus transcription is severely limited.