Li F Q, Takemaru K, Goto M, Ueda H, Handa H, Hirose S
Department of Developmental Genetics, National Institute of Genetics, Mishima, Shizuoka-ken, Japan.
Genes Cells. 1997 Feb;2(2):143-53. doi: 10.1046/j.1365-2443.1997.1090306.x.
Transcriptional activation of the Drosopohila melanogaster fushi tarzu gene by FTZ-F1 or its silkworm counterpart BmFTZ-F1 requires two cofactors MBF1 and MBF2 which do not directly bind to DNA. MBF1 is a bridging molecule that connects FTZ-F1 (or BmFTZ- F1), MBF2 and TATA binding protein TBP. MBF2 is a positive cofactor that activates transcription.
To elucidate the mechanism of transcriptional activation by MBF2, we isolated a cDNA coding for the factor. Northern blot analyses showed temporally restricted expression of MBF2 mRNA similar to that of BmFTZ-F1 mRNA. The cDNA sequence predicts a polypeptide of 10 kDa whereas natural MBF2 is a glycoprotein of 22 kDa. The deduced amino acid sequence of the factor showed no homology with proteins in the databases. Farwestern analyses and glutathione S-transferase interaction assays demonstrated that MBF2 makes a direct contact with the beta-subunit of TFIIA. In a HeLa cell nuclear extract, bacterially expressed recombinant MBF2 activated transcription from various promoters as natural MBF2 did. This activation requires the MBF2-TFIIA interaction. When recombinant MBF2 was added to the HeLa cell nuclear extract in the presence of MBF1 and FTZ622 bearing the DNA-binding region of FTZ-F1, it selectively activated transcription of the fushi tarazu gene. This selective activation also requires the MBF2-TFIIA interaction.
MBF2 activates transcription through its interaction with TFIIA. Selective transcriptional activation occurs when MBF2 is recruited to a promoter carrying the FTZ-F1 binding site by FTZ-F1 and MBF1.
果蝇的分节基因（fushi tarazu gene）由FTZ - F1或其家蚕对应物BmFTZ - F1进行转录激活需要两个辅助因子MBF1和MBF2，它们不直接与DNA结合。MBF1是一种桥梁分子，连接FTZ - F1（或BmFTZ - F1）、MBF2和TATA结合蛋白TBP。MBF2是一种激活转录的正辅助因子。
为阐明MBF2转录激活的机制，我们分离出编码该因子的cDNA。Northern印迹分析显示MBF2 mRNA的表达在时间上受到限制，类似于BmFTZ - F1 mRNA。该cDNA序列预测其编码一个10 kDa的多肽，而天然MBF2是一个22 kDa的糖蛋白。该因子推导的氨基酸序列与数据库中的蛋白质无同源性。Farwestern分析和谷胱甘肽S - 转移酶相互作用试验表明，MBF2与TFIIA的β亚基直接接触。在HeLa细胞核提取物中，细菌表达的重组MBF2与天然MBF2一样能激活各种启动子的转录。这种激活需要MBF2 - TFIIA相互作用。当在含有FTZ - F1 DNA结合区域的MBF1和FTZ622存在的情况下，将重组MBF2添加到HeLa细胞核提取物中时，它选择性地激活了分节基因的转录。这种选择性激活也需要MBF2 - TFIIA相互作用。
MBF2通过与TFIIA相互作用激活转录。当MBF2被FTZ - F1和MBF1招募到携带FTZ - F1结合位点的启动子时，发生选择性转录激活。
