Mazo A M, Huang D H, Mozer B A, Dawid I B
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 1990 Mar;87(6):2112-6. doi: 10.1073/pnas.87.6.2112.
The trithorax (trx) gene functions in segment determination in Drosophila through interaction with genes of the bithorax complex and Antennapedia complex. Genetic evidence suggests that trx may be considered a positive regulator of homeotic genes. Sequencing of cDNAs corresponding to the entire trx transcription unit revealed the existence of an unusually long open reading frame encoding 3759 amino acids. The main features of the predicted trx protein are several cysteine-rich regions which can be folded into zinc finger-like domains. Cysteine-rich portions expressed from trx cDNAs in Escherichia coli are capable of zinc binding in vitro, suggesting a possible function for the trx product as a metal-dependent DNA-binding protein. Analysis of trx mutant embryos with antibody to the Ultrabithorax (Ubx) gene product showed decreased staining in parasegment 6 of the ventral nerve cord of late embryos. However, expression of Ubx was not affected in embryos carrying the lethal mutation trxE3, in which one of the putative zinc finger-like domains of the trx protein is deleted. This differential effect of the E3 mutation suggests that trx exhibits other function(s) besides those involved in the regulation of Ubx expression in the ventral nerve cord of the embryo.
三体胸节（trx）基因在果蝇的体节决定过程中发挥作用，它通过与双胸复合体和触角足复合体的基因相互作用来实现。遗传学证据表明，trx可能被视为同源异型基因的正向调节因子。对对应于整个trx转录单元的cDNA进行测序，揭示了一个异常长的开放阅读框的存在，该开放阅读框编码3759个氨基酸。预测的trx蛋白的主要特征是几个富含半胱氨酸的区域，这些区域可以折叠成锌指样结构域。在大肠杆菌中由trx cDNA表达的富含半胱氨酸的部分能够在体外结合锌，这表明trx产物可能作为一种金属依赖性DNA结合蛋白发挥作用。用针对超双胸节（Ubx）基因产物的抗体对trx突变胚胎进行分析，结果显示晚期胚胎腹侧神经索的副节6中的染色减少。然而，在携带致死突变trxE3的胚胎中，Ubx的表达并未受到影响，在该突变中trx蛋白的一个假定锌指样结构域被删除。E3突变的这种差异效应表明，trx除了在胚胎腹侧神经索中参与调节Ubx表达的功能外，还表现出其他功能。
