Tsai-Morris C H, Geng Y, Buczko E, Dufau M L
Section on Molecular Endocrinology, NICHHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1995 Mar 31;270(13):7487-94. doi: 10.1074/jbc.270.13.7487.
Transcription of the luteinizing hormone receptor gene is dependent on Sp1-induced promoter activation from two Sp1 binding domains (Sp1(2), and Sp1(4)) within the 173-base pair promoter. Of the two Sp1 binding domains, the canonical GC box (GGGCGG) was determined by mutation to be the binding element for only the Sp1(2) domain. The Sp1 binding element within the Sp1(4) domain was identified by mutation and immunological/competition studies as the 5'-GGG GTG GGG that conforms to a Zif-268 like three zinc finger binding domain, rather than the canonical 3' Sp1(4) GC box (GGGCGG). The guanines in the third trinucleotide (GGG GTG GGG) were not required for Sp1 binding, although they increased binding affinity. Non-Sp1 protein(s) bind the 3' Sp1(4) GC box, and by themselves exhibit transcriptional activity. Tissue specific differences were localized to this non-Sp1 binding domain, which functionally substituted for the downstream activating M1 regulatory domain in non-expressing but not in expressing cells. Mutations of both non-Sp1 and M1 domains were required for inhibition of promoter activity in constructs that retained the Sp1 binding elements in non-expressing cells, indicating that together these domains may play a role in regulation of luteinizing hormone receptor gene expression.
促黄体生成素受体基因的转录依赖于173个碱基对启动子内两个Sp1结合域（Sp1(2)和Sp1(4)）所诱导的启动子激活。在这两个Sp1结合域中，通过突变确定典型的GC盒（GGGCGG）仅是Sp1(2)域的结合元件。通过突变以及免疫和竞争研究确定，Sp1(4)域内的Sp1结合元件是5'-GGG GTG GGG，它符合类Zif-268的三个锌指结合域，而不是典型的3' Sp1(4) GC盒（GGGCGG）。尽管第三三核苷酸（GGG GTG GGG）中的鸟嘌呤增加了结合亲和力，但Sp1结合并不需要它们。非Sp1蛋白结合3' Sp1(4) GC盒，并且自身表现出转录活性。组织特异性差异定位于这个非Sp1结合域，在非表达细胞中它在功能上替代了下游激活的M1调节域，但在表达细胞中则不然。在非表达细胞中保留Sp1结合元件的构建体中，抑制启动子活性需要同时突变非Sp1和M1域，这表明这些域可能共同在促黄体生成素受体基因表达的调控中发挥作用。
