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Activation of adenovirus promoters by the adenovirus E1A protein in cell-free extracts
Abstract:
The primary product of the adenovirus E1A gene is a protein that is sufficient for controlling host-cell proliferation and immortalizing primary rodent cells. The mechanism by which the protein induces these cellular effects is poorly understood, but might be linked to its ability to regulate RNA transcription from a number of viral and cellular genes. The mechanism of E1A's transcriptional-activation (trans-activation) was studied here by monitoring the protein's effect on specific adenovirus promoters in two types of transcriptional systems in vitro. One of these systems consisted of extracts from transformed cells constitutively expressing E1A, and the other consisted of extracts of HeLa cells supplemented with a plasmid-encoded E1A protein purified from Escherichia coli. The results show that the E1A protein specifically stimulates transcription from adenovirus promoters; thus, the induction of cellular transcription factors is not necessary to explain the stimulation of transcription by E1A.
Insights
Adenovirus E1A protein controls cell proliferation and immortalization. This study shows E1A directly stimulates viral gene transcription without needing new cellular transcription factors.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- The adenovirus E1A gene product influences host cell proliferation and immortalization.
- The precise mechanism of E1A's transcriptional regulation is not fully understood.
- E1A's role in regulating RNA transcription from viral and cellular genes is a key area of investigation.
Purpose of the Study:
- To investigate the mechanism of E1A-mediated transcriptional activation (trans-activation).
- To determine if E1A directly affects transcription from adenovirus promoters.
- To assess the necessity of induced cellular transcription factors for E1A's trans-activation function.
Main Methods:
- Studied E1A's effect on adenovirus promoters using in vitro transcriptional systems.
- Utilized cell extracts from E1A-expressing transformed cells.
- Employed HeLa cell extracts supplemented with purified, plasmid-encoded E1A protein.
Main Results:
- The E1A protein was observed to specifically stimulate transcription from adenovirus promoters.
- This stimulation occurred in both tested transcriptional systems.
- The results indicate that E1A can activate transcription independently of inducing new cellular factors.
Conclusions:
- E1A protein directly activates transcription from adenovirus promoters.
- The induction of cellular transcription factors is not required for E1A-mediated transcriptional stimulation.
- E1A's direct action on viral promoters is a key mechanism for its cellular effects.