Regulation of TAFII250 Activity by TAFII55

通用转录因子TFIID由TATA结合蛋白(TBP)和一系列TBP相关因子(TAFs)组成，TBP相关因子共同参与转录预起始复合体的组装。其中一个TAFs TAFII250具有转录MHC I类基因所必需的乙酰转移酶(AT)活性：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，筛选了一个具有TAFII250片段(848-1279AA)的酵母双杂交文库，该片段跨越其AT结构域和RAP74结合域的一部分。TFIID组分TAFII55被分离出来，并发现主要与RAP74结合结构域相互作用。TAFII55与TAFII250结合可抑制其AT活性。重要的是，在体外转录实验中加入重组TAFII55可以抑制依赖TAFII250的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的生物学作用正在通过研究体外组装的预起始复合体(PIC)的转录来研究，其中TAFII55可以与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.