Haviv I, Shamay M, Doitsh G, Shaul Y
Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.
Mol Cell Biol. 1998 Mar;18(3):1562-9. doi: 10.1128/MCB.18.3.1562.
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.
乙肝病毒（HBV）编码的调节因子pX通过未知机制共激活转录。pX与转录机制的多个组分相互作用，包括某些激活因子、TFIIB、TFIIH以及RNA聚合酶II（POLII）。我们发现pX定位于细胞核，并能与核提取物中的TFIIB进行共免疫沉淀。我们使用了在结合POLII或TATA结合蛋白方面无活性的TFIIB突变体，来研究TFIIB-pX相互作用在转录共激活中的作用。pX能够结合前一种类型的TFIIB突变体，而不能结合后一种。这两组TFIIB突变体均不支持转录。值得注意的是，后一组TFIIB突变体完全阻断了pX的活性，提示TFIIB在pX介导的共激活中的作用。相比之下，在pX存在的情况下，POLII结合被破坏的TFIIB突变体在体内和体外均获得了野生型表型。这些结果表明，pX可能通过充当分子桥梁来建立原本低效的TFIIB突变体-POLII相互作用。总体而言，我们的结果证明TFIIB是pX在体内的作用靶点。
