Jain S, Dolwick K M, Schmidt J V, Bradfield C A
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611.
J Biol Chem. 1994 Dec 16;269(50):31518-24.
The Ah receptor (AHR) is a ligand-activated transcription factor that is structurally related to its dimerization partner, the Ah receptor nuclear translocator (ARNT), and two Drosophila proteins, SIM and PER. All four proteins contain a region of homology now referred to as a PAS homology domain. In addition, the AHR, ARNT, and SIM harbor a basic region helix-loop-helix motif in their N termini, whereas PER does not. Previous mapping studies of the AHR have demonstrated that the PAS domain contains sequences required for ligand recognition, dimerization, and interaction with the 90-kDa heat shock protein. They also have confirmed that the basic region helix-loop-helix domain plays a role in both dimerization and sequence-specific DNA binding. To identify domains involved in transactivation of target genes, we generated chimeras of AHR/ARNT deletion mutants with the DNA binding region of the yeast Gal4 protein, transiently expressed these in COS-1 cells, and monitored their capacity to activate the chloramphenicol acetyltransferase reporter gene under the control of a minimal promoter driven by enhancer elements recognized by Gal4. Extensive analysis of these fusions revealed that the AHR and ARNT harbor potent transactivation domains within their C termini. Importantly, the amino-terminal halves of both the AHR and ARNT were found to be devoid of transactivation activity.
芳烃受体（AHR）是一种配体激活的转录因子，在结构上与其二聚化伴侣芳烃受体核转运蛋白（ARNT）以及两种果蝇蛋白SIM和PER相关。这四种蛋白都含有一个现在被称为PAS同源结构域的同源区域。此外，AHR、ARNT和SIM在其N端含有一个碱性区域螺旋-环-螺旋基序，而PER则没有。先前对AHR的定位研究表明，PAS结构域包含配体识别、二聚化以及与90 kDa热休克蛋白相互作用所需的序列。这些研究还证实，碱性区域螺旋-环-螺旋结构域在二聚化和序列特异性DNA结合中都发挥作用。为了鉴定参与靶基因反式激活的结构域，我们构建了AHR/ARNT缺失突变体与酵母Gal4蛋白DNA结合区域的嵌合体，在COS-1细胞中瞬时表达这些嵌合体，并监测它们在由Gal4识别的增强子元件驱动的最小启动子控制下激活氯霉素乙酰转移酶报告基因的能力。对这些融合体的广泛分析表明，AHR和ARNT在其C端含有有效的反式激活结构域。重要的是，发现AHR和ARNT的氨基末端一半都没有反式激活活性。
