Dela Cruz F, Mak P
American Cyanamid Company, Agricultural Research Division, Princeton, NJ 08540, USA.
J Steroid Biochem Mol Biol. 1997 Jul;62(4):353-9. doi: 10.1016/s0960-0760(97)00046-0.
Transcriptional activation of the Drosophila ecdysone receptor (EcR) was studied in yeast cells, which carry a reporter plasmid containing the ecdysone response element in the absence or presence of its heterodimeric partners, ultraspiracle protein (USP) or human retinoid X receptor (RXRalpha). High constitutive transcriptional activation was detected in the yeast strain expressing EcR, but not USP or RXRalpha in the absence of ponasterone or muristerone A. Incubation of these ligands with yeast cells coexpressing EcR and USP or RXRalpha did not enhance the constitutive transcriptional activity. However, specific ligand binding using [3H]ponasterone A as a radioactive ligand was detected only in yeast extracts prepared from the yeast strain coexpressing EcR and USP, but not from yeast strains expressing only EcR or USP. The ligand binding characteristics of the EcR/USP complexes were similar to those reported in an insect cell line with a Kd value of 1.8 nM for [3H]ponasterone A. These data are in contrast to mammalian cell transfection studies, and indicate that the EcR is the only member of the nuclear receptor superfamily of ligand-activated transcription factors which functions as a constitutive transcriptional activator in yeast, although the EcR/USP complexes exhibit normal ligand binding properties.
在酵母细胞中研究了果蝇蜕皮激素受体（EcR）的转录激活，这些酵母细胞携带一个含有蜕皮激素反应元件的报告质粒，且存在或不存在其异二聚体伴侣超气门蛋白（USP）或人类视黄酸X受体（RXRα）。在缺乏蜕皮甾酮或莫尼酮A的情况下，在表达EcR但不表达USP或RXRα的酵母菌株中检测到高组成型转录激活。将这些配体与共表达EcR和USP或RXRα的酵母细胞一起孵育不会增强组成型转录活性。然而，仅在从共表达EcR和USP的酵母菌株制备的酵母提取物中检测到使用[3H]蜕皮甾酮A作为放射性配体的特异性配体结合，而在仅表达EcR或USP的酵母菌株中未检测到。EcR/USP复合物的配体结合特性与在昆虫细胞系中报道的相似，[3H]蜕皮甾酮A的Kd值为1.8 nM。这些数据与哺乳动物细胞转染研究形成对比，并表明EcR是配体激活转录因子核受体超家族中唯一在酵母中作为组成型转录激活剂起作用的成员，尽管EcR/USP复合物表现出正常的配体结合特性。
