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Vaccinia virus gene A18R DNA helicase is a transcript release factor
1Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida 32610-0266, USA.
The Journal of Biological Chemistry
|January 8, 2000
Summary
Vaccinia virus protein A18R is essential for releasing nascent RNA during transcription elongation. It requires an unidentified cellular factor and ATP to function, indicating a role in regulating viral gene expression.
Area of Science:
- Virology
- Molecular Biology
- Biochemistry
Background:
- Phenotypic analysis of vaccinia virus gene A18R mutant (Cts23) revealed longer viral transcripts, suggesting A18R negatively regulates transcription elongation.
- Understanding the biochemical activity of A18R is crucial for elucidating vaccinia virus transcription regulation.
Purpose of the Study:
- To determine the biochemical activity of the vaccinia virus A18R protein.
- To investigate the role of A18R in nascent RNA release from transcription elongation complexes.
Main Methods:
- Assay of pulse-labeled transcription complexes from intermediate virus promoters on bead-bound DNA.
- Analysis of transcript release in the presence of nucleotides, wild-type (Wt) extract, Cts23 extract, and purified His-A18R protein.
- Investigation of ATP dependence for transcript release.
Main Results:
- Wild-type extract induced nascent RNA release, while Cts23 extract did not, implicating A18R in this process.
- Purified His-A18R alone did not induce release, but did so in combination with mock or Cts23 extract.
- A18R is necessary but not sufficient for transcript release; release is ATP-dependent and occurs across all viral promoter classes.
Conclusions:
- Vaccinia virus A18R protein, along with an unidentified cellular factor, is required for in vitro release of nascent RNA.
- A18R functions as an ATP-dependent helicase involved in regulating transcription elongation complex dynamics.