Kirov N, Zhelnin L, Shah J, Rushlow C
Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110.
EMBO J. 1993 Aug;12(8):3193-9. doi: 10.1002/j.1460-2075.1993.tb05988.x.
The dorsal (dl) protein gradient determines patterns of gene expression along the dorsal-ventral axis of the Drosophila embryo. dl protein is at peak levels in ventral nuclei of the embryo where it activates some genes (twist and snail) and represses others [zerknullt (zen), decapentaplegic and tolloid]. It is a member of the rel family of transcription factors and interacts with specific DNA sequences in the regulatory regions of its target genes. These sequences (dl binding sites), when taken from the context of either an activated or repressed promoter, mediate transcriptional activation of a heterologous promoter, but not repression. We found that T-rich sequences close to the dl binding sites in the silencer region of the zen promoter are conserved between three Drosophila species. Using this sequence information we defined a minimal element that can mediate repression of a heterologous promoter. This element interacts with at least two factors present in embryonic extracts, one of which is dl protein. The other factor binds to the T-rich site. Point mutations in either site abolish ventral repression in vivo. In addition, mutations in the T-rich site cause ectopic expression in ventral regions indicating that the minimal silencer was converted into an enhancer.
背侧（dl）蛋白梯度决定了果蝇胚胎背腹轴上的基因表达模式。dl蛋白在胚胎的腹侧细胞核中处于峰值水平，在那里它激活一些基因（twist和snail）并抑制其他基因[零化（zen）、果蝇转化生长因子β（decapentaplegic）和类原肠胚形成蛋白（tolloid）]。它是转录因子rel家族的成员，并与其靶基因调控区域中的特定DNA序列相互作用。这些序列（dl结合位点），当从激活或抑制的启动子背景中提取时，介导异源启动子的转录激活，但不介导抑制。我们发现，在zen启动子沉默区域中靠近dl结合位点的富含T的序列在三种果蝇物种之间是保守的。利用这些序列信息，我们定义了一个可以介导异源启动子抑制的最小元件。该元件与胚胎提取物中存在的至少两种因子相互作用，其中一种是dl蛋白。另一种因子与富含T的位点结合。任一位点的点突变都会在体内消除腹侧抑制。此外，富含T的位点的突变会导致腹侧区域的异位表达，这表明最小沉默子已转化为增强子。
