Liaw G J, Steingrimsson E, Pignoni F, Courey A J, Lengyel J A
Department of Biology, University of California, Los Angeles 90024.
Proc Natl Acad Sci U S A. 1993 Feb 1;90(3):858-62. doi: 10.1073/pnas.90.3.858.
At the poles of the Drosophila embryo, cell fate is established by a pathway that begins with the activation of a membrane-associated tyrosine kinase (the torso gene product); this then leads to activation of a serine/threonine kinase (Drosophila Raf-1). Activated Raf-1 then leads, by an undefined mechanism, to the transcriptional activation of the tailless (tll) gene; the tll gene product, itself a transcription factor, subsequently regulates the expression of an array of target genes. To further define this pathway, we have utilized sequence comparison between Drosophila melanogaster and Drosophila virilis to identify conserved elements in the tll promoter region. As assessed by DNase I footprinting and promoter dissection experiments, two of these elements are potential regulatory targets of Raf-1-activated transcription factors. Sequence comparison also reveals that the unique residues in the DNA-binding domain of the tll protein, the next component in the pathway, are conserved. One of these residues, the alanine after the last cysteine in the first zinc finger, may be responsible for part of the difference between the tll protein DNA binding site and the closely related half-site of the retinoid/estrogen receptors. Consistent with the rapid turnover of the tll protein, it contains a PEST sequence (rich in proline, glutamate and aspartate, serine, and threonine) that is also conserved.
在果蝇胚胎的两极，细胞命运是由一条始于膜相关酪氨酸激酶（躯干基因产物）激活的信号通路决定的；这随后导致丝氨酸/苏氨酸激酶（果蝇Raf-1）的激活。激活的Raf-1然后通过一种未知机制导致无尾（tll）基因的转录激活；tll基因产物本身是一种转录因子，随后调节一系列靶基因的表达。为了进一步明确这条信号通路，我们利用黑腹果蝇和 virilis果蝇之间的序列比较来鉴定tll启动子区域中的保守元件。通过DNase I足迹分析和启动子剖析实验评估，其中两个元件是Raf-1激活的转录因子的潜在调控靶点。序列比较还显示，该信号通路中下一个组分tll蛋白的DNA结合结构域中的独特残基是保守的。其中一个残基，即第一个锌指中最后一个半胱氨酸后的丙氨酸，可能是tll蛋白DNA结合位点与类视黄醇/雌激素受体密切相关的半位点之间部分差异的原因。与tll蛋白的快速周转一致，它包含一个同样保守的PEST序列（富含脯氨酸、谷氨酸、天冬氨酸、丝氨酸和苏氨酸）。
