Regulation of TAFII250 Activity by TAFII55

一般转录因子TFIID由TATA结合蛋白（TBP）和一系列TBP相关因子（TAFs）组成，这些因子共同参与转录起始前复合物的组装。其中一种TAFs TAFII250具有乙酰转移酶（AT）活性，这是MHC I类基因转录所必需的：抑制AT活性会抑制转录。为了确定可能调节TAFII250 AT活性的潜在细胞因子，我们筛选了一个酵母双杂交文库，其中TAFII250片段（848-1279 aa）跨越了部分AT域和RAP74结合域。TFIID成分TAFII55被分离出来，发现主要与rap74结合域相互作用。TAFII55结合TAFII250抑制其AT活性。重要的是，在体外转录检测中加入重组TAFII55可抑制tafii250依赖性MHC I类转录。因此，TAFII55能够通过调节其AT活性来调节TAFII250的功能。TAFII55抑制TAFII250的生物学作用是通过研究体外组装的预起始复合物（PIC）的转录来研究的，其中可以表明TAFII55与PIC组装。

The general transcription factor, TFIID, consists of the TATA binding protein (TBP) associated with a series of TBP-associated factors (TAFs) that together participate in the assembly of the transcription preinitiation complex. One of the TAFs, TAFII250, has acetyl transferase (AT) activity that is necessary for transcription of MHC class I genes: inhibition of the AT activity represses transcription. To identify potential cellular factors that might regulate the AT activity of TAFII250, a yeast two-hybrid library was screened with a TAFII250 segment (848-1279 aa) that spanned part of its AT domain and its RAP74 binding domain. The TFIID component, TAFII55, was isolated and found to interact predominantly with the RAP74-binding domain. TAFII55 binding to TAFII250 inhibits its AT activity. Importantly, addition of recombinant TAFII55 to in vitro transcription assays inhibits TAFII250-dependent MHC class I transcription. Thus, TAFII55 is capable of regulating TAFII250 function by modulating its AT activity. The biological role of TAFII55-repression of TAFII250 is being investigated by studying transcription of in vitro assembled pre-initiation complexes (PIC), in which it can be shown that TAFII55 assembles with the PIC.