Molecular mechanism for general regulation on transcription

我们先前发现了一种新的TBP相互作用蛋白(TIP 120)，该蛋白来自大鼠肝脏。在本研究中，我们证明了重组TIP 120激活了各种启动子的基础转录水平，而与模板DNA拓扑结构以及TFIIE/TFIIH和TAFs的存在无关。动力学研究表明，TIP 120在RNAP II/TFIIF向启动子募集时形成预引发复合体的过程中发挥作用，但在预引发复合体(PIG)形成完成后不起作用。EMSA表明，TIP 120通过克服RNAP II/TFIIF整合到TBP/TFIIB-DNA-复合体的动力学障碍，促进了猪的形成。缺失分析表明，TIP120功能所需的N-末端412残基包括一个酸性区域和TBP结合区。有趣的是，TIP 120在体外也刺激了RNAP I和Ill驱动的转录。在小鼠细胞中，异位表达的TIP 120增强了所有三类启动子(I、II和III类)的转录。经维甲酸处理后，TIP 120核染色图案由锐斑变为大斑点。此外，Hep-2细胞中的大约TIP 120区域与PML癌基因段共定位。

We previously identified a novel TBP-interacting protein (TIP 120 from rat liver. In this study, we demonstrated that recombinant TIP 120 activated the basal level of transcription from various kinds of promoters regardless of the template DNA topology and the presence of TFIIE/TFIIH and TAFs. Kinetic studies suggested that TIP 120 functioned during preinitiation complex formation at the step of RNAP II/TFIIF recruitment to the promoter, but not after the completion of preinitiation complex (PIG) formation. EMSA showed that TIP 120 enhanced PIG formation by overcoming a kinetic impediment to RNAP II/TFIIF integration into the TBP/TFIIB- DNA-complex. Deletion analysis demonstrated that the N-terminal 412 residues including an acidic region and the TBP-binding domain is required for TIP120 function. Interestingly, TIP 120 also stimulated RNAP I- and Ill-driven transcription in vitro. In mouse cells, ectopically expressed TIP 120 enhanced transcription from all three classes (class I, II, and III) of promoters. The TIP 120 nuclear staining patterns changed from sharp foci to large speckles upon retinoic acid treatment. Moreover, some TIP 120 regions in HEp-2 cells were colocalized with the PML oncogenic domains.