Haviv I, Vaizel D, Shaul Y
Department of Molecular Genetics and Virology, The Weizmann Institute of Science, Rehovot, Israel.
EMBO J. 1996 Jul 1;15(13):3413-20.
The X protein of hepatitis B virus (HBV) coactivates activators bearing potent (mostly acidic) activation domains. Here, we investigated the molecular mechanisms of this coactivation. We show that pX interacts with general transcription factors TFIIB and TFIIH, as well as with the potent activation domain of VP16. TFIIB interacts with both pX and VP16 simultaneously. In addition, the RNA polymerase II enzyme itself binds to pX. By reducing the activity of cellular coactivators, through squelching, we intensify the dependence of the activator on pX-mediated coactivation. Squelching is essentially diminished in the presence of pX, both in vivo and in vitro. The target of pX in this activity is the template-bound activator, and not the squelcher. Furthermore, by following transcription in a TAF-deprived reaction, we demonstrate absolute dependence of the activator on the activity of pX. We propose that pX coactivates transcription by substituting cellular coactivators in activator-preinitiation complex interactions.
乙型肝炎病毒（HBV）的X蛋白可共激活带有强效（大多为酸性）激活域的激活剂。在此，我们研究了这种共激活的分子机制。我们发现pX与通用转录因子TFIIB和TFIIH相互作用，还与VP16的强效激活域相互作用。TFIIB同时与pX和VP16相互作用。此外，RNA聚合酶II自身也与pX结合。通过抑制细胞共激活剂的活性，我们增强了激活剂对pX介导的共激活的依赖性。在体内和体外，在pX存在的情况下，抑制作用基本减弱。pX在该活性中的作用靶点是与模板结合的激活剂，而非抑制物。此外，通过在缺乏TAF的反应中跟踪转录过程，我们证明了激活剂对pX活性的绝对依赖性。我们提出，pX通过在激活剂-预起始复合物相互作用中替代细胞共激活剂来共激活转录。
