Function of basal transcription factor TFIIA as coactivator

转录起始是基因表达最重要的步骤。起始反应受基因特异性转录因子与RNA聚合酶II等基础转录因子相互作用的调控，基础转录因子形成前起始复合物（preinitiation complex，PIC）。我们对TFIIA的结构和功能进行了分析，阐明了TFIIA是一种基础转录因子，通过桥接激活因子和PIC而发挥共激活因子的作用。TFIIA被认为是通过与TFIID结合来调节基础转录活性。固定的乳胶珠和使用该珠从HeLa细胞核提取物纯化的人TFIIA（Shiroya等，国际生物色谱学杂志，1：191- 198，1995）。我们确定了37 kD亚基的部分氨基酸序列并分离了其cDNA克隆（Ma.et al.，基因开发，7：2246- 2257，1993）。我们已经表明，TFIIA释放Dr 2介导的转录抑制和共激活Ga 14-VP 16介导的转录激活。FTZ-F1是果蝇fushi tarazu基因表达的激活剂。BmFTZ-F1是FTZ-F1的蚕对应物。最近，MBF 1和MBF 2已被确定为BmFTZ-F1的共活化剂。MBF 1与BmFTZ-F1和TBP相互作用，我们阐明MBF 2与MBF 1和TFIIA相互作用（Li，F-Q.，例如，提交）。这一结果证实了TFIIA通过在激活剂和PIC之间桥接而作为共激活剂起作用。

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.