Hepatitis B virus pX targets TFIIB in transcription coactivation.
pX, the hepatitis B virus (HBV)-encoded regulator, coactivates transcription through an unknown mechanism. pX interacts with several components of the transcription machinery, including certain activators, TFIIB, TFIIH, and the RNA polymerase II (POLII) enzyme. We show that pX localizes in the nucleus and coimmunoprecipitates with TFIIB from nuclear extracts. We used TFIIB mutants inactive in binding either POLII or TATA binding protein to study the role of TFIIB-pX interaction in transcription coactivation. pX was able to bind the former type of TFIIB mutant and not the latter. Neither of these sets of TFIIB mutants supports transcription. Remarkably, the latter TFIIB mutants fully block pX activity, suggesting the role of TFIIB in pX-mediated coactivation. By contrast, in the presence of pX, TFIIB mutants with disrupted POLII binding acquire the wild-type phenotype, both in vivo and in vitro. These results suggest that pX may establish the otherwise inefficient TFIIB mutant-POLII interaction, by acting as a molecular bridge. Collectively, our results demonstrate that TFIIB is the in vivo target of pX.
Haviv
I
I
Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.
Shamay
M
M
Doitsh
G
G
Shaul
Y
Y
D002457:Cell Extracts; D002467:Cell Nucleus / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D015967:Gene Expression Regulation, Viral; D006515:Hepatitis B virus / Q000378:metabolism*; D016296:Mutagenesis; D011233:Precipitin Tests; D015534:Trans-Activators / Q000378:metabolism*; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D054334:Viral Regulatory and Accessory Proteins; D016335:Zinc Fingers / Q000235:genetics
D002457:Cell Extracts; D015534:Trans-Activators; D035581:Transcription Factor TFIIB; D014157:Transcription Factors; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein