Petersen U M, Björklund G, Ip Y T, Engström Y
Department of Molecular Biology, Arrhenius Laboratories for Natural Sciences, Stockholm University, Sweden.
EMBO J. 1995 Jul 3;14(13):3146-58. doi: 10.1002/j.1460-2075.1995.tb07317.x.
A new member of the Rel family of transcription factors, the dorsal-related immunity factor, Dif, was recently cloned and suggested to be involved in regulating the immune response in Drosophila. Despite its classification as a Rel family member, the Dif cDNA-encoded product has not been proven previously to be a transcription factor. We now present evidence that the Dif gene product trans-activates the Drosophila Cecropin A1 gene in co-transfection assays. The transactivation requires a 40 bp upstream element including an insect kappa B-like motif. A dimer of the kappa B-like motif 5'-GGGGATTTTT inserted into a minimal promoter conferred high levels of reporter gene expression by Dif, while a multimer of several mutated versions of this motif was not activated, demonstrating the sequence specificity of Dif. Full trans-activation by Dif requires the C-terminal part of the protein. The morphogen dorsal (dl) can also activate the Cecropin A1 promoter, but to a lesser extent and in a less sequence-specific manner than Dif. Simultaneous overexpression of Dif and dl in co-transfection assays revealed that dl possesses a dominant negative effect on Dif transactivation. This study establishes that Dif is a sequence-specific transcription factor and is probably a key activator of the immune response in Drosophila.
转录因子Rel家族的一个新成员，即背侧相关免疫因子Dif，最近被克隆出来，并被认为参与调控果蝇的免疫反应。尽管Dif被归类为Rel家族成员，但其cDNA编码产物此前尚未被证实是一种转录因子。我们现在提供证据表明，在共转染实验中，Dif基因产物可反式激活果蝇杀菌肽A1基因。这种反式激活需要一个包含昆虫κB样基序的40 bp上游元件。插入最小启动子中的κB样基序5'-GGGGATTTTT的二聚体可使Dif介导报告基因高水平表达，而该基序几个突变版本的多聚体则未被激活，这证明了Dif的序列特异性。Dif的完全反式激活需要该蛋白的C末端部分。形态发生素背侧（dl）也可激活杀菌肽A1启动子，但程度低于Dif，且序列特异性也不如Dif。在共转染实验中同时过表达Dif和dl表明，dl对Dif反式激活具有显性负效应。这项研究证实Dif是一种序列特异性转录因子，可能是果蝇免疫反应的关键激活因子。
