Function of basal transcription factor TFIIA as coactivator

转录起始是基因表达最重要的步骤。启动反应受基因特异性转录因子和包括RNA聚合酶II在内的基础转录因子相互作用的调节。我们分析了基础转录因子之一TFIIA的功能和结构，阐明了TFIIA通过激活因子与PIC之间的桥梁起到了共激活的作用。人TFIIA由三个亚基组成，分子量分别为37kD、19kD、13kD。TFIIA被认为通过与TFIID结合来调节基础转录活性。我们测定了37kD亚基的部分氨基酸序列，并分离了其cDNA克隆(Ma.et al.，gene Dev.，7：2246-2257,1993)。我们发现TFIIA释放了DR2介导的转录抑制，并共同激活了Ga14-VP16介导的转录激活。FTZ-F1是一种刺激果蝇福氏蒲公英基因表达的激活剂。BmFTZ-F1是FTZ-F1的家蚕。最近，MBF1和MBF2被确定为BmFTZ-F1的共激活因子。MBF1与BmFTZ-F1和TBP都有相互作用。我们阐明了MBF2既与MBF1相互作用，又与TFIIA相互作用(Li，F-Q等，提交)。这一结果证实了TFIIA通过连接激活剂和PIC起到了共激活剂的作用。

Transcription initiation is the most important step of gene expression. The reaction of initiation is regulated by interactions between gene-specific transcription factors and basal transcription factors including RNA polymerase II.Basal transcription factors fromed the preinitiation complex (PIC). We analyzed function and structure of TFIIA,one of the basal transcription factors, and elucidated that TFIIA worked as a coactivator through bridging between activators and PIC.Human TFIIA is composed of three subunits with the molecular weights of 37kD,19kD,13kD.TFIIA has been thought to regulate basal transcription activity by binding to TFIID.We made recombinant TBP-fixed latex beads and purified human TFIIA from HeLa cell nuclear extracts by using the beads (Shiroya et al., Internl.J.Bio-chromatog., 1 : 191-198,1995). We determined partial amino acid sequences of the 37kD subunit and isolated its cDNA clone (Ma.et al., Genes Dev., 7 : 2246-2257,1993). We have showed that TFIIA released Dr2-mediated suppression of transcription and coactivated Ga14-VP16-mediated transcription activation. FTZ-F1 is an activator which stimulate expression of the fushi tarazu gene of Drosophila. BmFTZ-F1 is the silk-worm counterpart of FTZ-F1. Recently, MBF1 and MBF2 have been identified as coactivators of BmFTZ-F1. MBF1 has been shown to interact with both BmFTZ-F1 and TBP.We elucidatethat MBF2 interacts with both MBF1 and TFIIA (Li, F-Q., et al., submitted). This result confirms that TFIIA worked as a coactivator through bridging between activator and PIC.