Forsberg M, Ström A C, Lillhager P, Westin G
Department of Medical Genetics, Uppsala University, Sweden.
Biol Chem Hoppe Seyler. 1995 Nov;376(11):661-9. doi: 10.1515/bchm3.1995.376.11.661.
To localize regions in the human transcription factor Sp1, which are involved in activating transcription of the U2 snRNA gene promoter and of a TATA box gene promoter, the activation potentials of GAL4/Sp1 chimeras were analyzed in mammalian cells. In vitro mutagenesis analysis of Sp1 showed that mutation of a hydrophobic amino acid residue in glutamine-rich activation domain A impairs stimulation of transcription from the TATA box promoter, but not from the U2 promoter. Furthermore, we found that similar parts of Sp1 are involved in synergistic activation of transcription together with the SV40 enhancer and with an enhancer which binds a single type of transcription factor. This suggests that the activating mechanism of Sp1 is the same with both enhancers. Interestingly, we found that the glutamine-rich domains A and B, that stimulate transcription from the TATA box promoter were not sufficient for U2 gene activation. Stimulation of U2 transcription required amino acid residues 231-485 of Sp1, which contain the glutamine-rich domain B and a serine/threonine-rich part. Since overlapping, but non-identical parts of Sp1 are required for activation of the two promoter types, we conclude that Sp1 activates the U2 snRNA and TATA box promoters by different mechanisms.
为了定位人类转录因子Sp1中参与激活U2 snRNA基因启动子和TATA框基因启动子转录的区域，我们在哺乳动物细胞中分析了GAL4/Sp1嵌合体的激活潜能。对Sp1的体外诱变分析表明，富含谷氨酰胺的激活结构域A中一个疏水氨基酸残基的突变会损害TATA框启动子的转录刺激，但不会损害U2启动子的转录刺激。此外，我们发现Sp1的相似部分与SV40增强子以及与结合单一类型转录因子的增强子一起参与转录的协同激活。这表明Sp1与两种增强子的激活机制相同。有趣的是，我们发现刺激TATA框启动子转录的富含谷氨酰胺的结构域A和B不足以激活U2基因。刺激U2转录需要Sp1的231 - 485位氨基酸残基，其中包含富含谷氨酰胺的结构域B和富含丝氨酸/苏氨酸的部分。由于激活两种启动子类型需要Sp1重叠但不相同的部分，我们得出结论，Sp1通过不同机制激活U2 snRNA启动子和TATA框启动子。
