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Infection of terminally differentiated myotubes with Rous sarcoma virus: reduced synthesis of env and v-src proteins
1Department of Microbiology, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Abstract:
We studied Rous sarcoma virus (RSV) protein synthesis in RSV-infected, terminally differentiated chicken myotubes ('late-infected' myotubes), in which no viral DNA integration takes place but all three viral mRNAs (38S, 28S and 21S) are transcribed normally. With the use of specific anti-RSV protein antisera, we found that only the viral gag and pol proteins were synthesized at levels similar to those synthesized in RSV-transformed fibroblasts; the synthesis of env and v-src proteins was significantly reduced in these infected myotubes. We concluded that the viral RNA transcribed from the unintegrated RSV DNA was functional but that genes at the 3' end of the RSV genome were translated at a lower level. By contrast, when mononucleated replicating chicken myoblasts were infected with a mutant (tsNY68) carrying a temperature-sensitive v-src gene and maintained at the non-permissive temperature for this gene, they developed into myotubes with viral DNA integrated in their chromosomal DNA. These 'early-infected' myotubes expressed all four viral genes (gag, pol, env and v-src) at a level similar to that in infected fibroblasts. This result ruled out the possible presence of specific factor(s) in myotubes that preferentially inhibit the 3' genes of RSV, and suggested other translational control(s) of viral gene expression in late-infected myotubes.
Insights
Chicken myotubes infected with Rous sarcoma virus (RSV) show reduced synthesis of viral env and v-src proteins. This suggests translational control mechanisms limit the expression of 3' end viral genes from unintegrated DNA.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Rous sarcoma virus (RSV) infects chicken cells, leading to viral protein synthesis.
- Viral gene expression regulation is crucial for understanding viral replication and pathogenesis.
- Chicken myotubes offer a model system to study viral gene expression in differentiated cells.
Purpose of the Study:
- To investigate Rous sarcoma virus (RSV) protein synthesis in terminally differentiated chicken myotubes.
- To determine the translational efficiency of different viral genes in RSV-infected myotubes.
- To elucidate the regulatory mechanisms controlling viral gene expression in differentiated muscle cells.
Main Methods:
- Infection of terminally differentiated chicken myotubes with RSV.
- Analysis of viral mRNA transcription and protein synthesis using specific anti-RSV protein antisera.
- Infection of chicken myoblasts with a temperature-sensitive RSV mutant (tsNY68) to study viral DNA integration and gene expression.
Main Results:
- In RSV-infected, terminally differentiated myotubes (late-infected), gag and pol protein synthesis was normal, but env and v-src synthesis was significantly reduced.
- Viral RNA transcribed from unintegrated RSV DNA was functional, but genes at the 3' end were translated at lower levels.
- RSV-infected myotubes with integrated viral DNA (early-infected) expressed all viral genes (gag, pol, env, v-src) at normal levels, similar to infected fibroblasts.
Conclusions:
- Translational control mechanisms preferentially affect the expression of 3' end genes of the RSV genome in terminally differentiated myotubes with unintegrated viral DNA.
- The results rule out specific inhibitory factors in myotubes that target RSV 3' genes.
- Differential translational control regulates viral gene expression in RSV-infected differentiated chicken myotubes.