Scaffidi P, Bianchi M E
San Raffaele Scientific Institute, via Olgettina 58, 20132 Milan, Italy.
J Biol Chem. 2001 Dec 14;276(50):47296-302. doi: 10.1074/jbc.M107619200. Epub 2001 Oct 2.
Sox proteins, a subclass of high mobility group box proteins, govern cell fate decisions by acting both as classical transcription factors and architectural components of chromatin. We aimed to demonstrate that the DNA bending activity of Sox proteins is essential to regulate gene expression. We focused on mouse Sox2, which participates in the transactivation of the Fgf4 (fibroblast growth factor 4) gene in the inner cell mass of the blastocyst. We generated six substitutions in the high mobility group box of Sox2. One mutant showed a reduced DNA bending activity on the Fgf4 enhancer (46 degrees instead of 80 degrees), which resulted in more powerful transactivation compared with the wild type protein. We then selected two single-base mutations in the Fgf4 enhancer that make the DNA less bendable by the Sox2 protein. Again, a different DNA bend (0 degrees and 42 degrees instead of 80 degrees) resulted in a different activation of transcription, but in this case reduced bending corresponded to decreased transcription. We found that the opposite effect on transcription of similar DNA bending angles is due to a 20 degrees difference in the relative orientation of the DNA bends, proving that a correct three-dimensional geometry of enhanceosome complexes is necessary to promote transcription.
Sox蛋白是高迁移率族框蛋白的一个亚类，它既作为经典转录因子又作为染色质的结构成分来决定细胞命运。我们旨在证明Sox蛋白的DNA弯曲活性对于调节基因表达至关重要。我们聚焦于小鼠Sox2，它参与胚泡内细胞团中Fgf4（成纤维细胞生长因子4）基因的反式激活。我们在Sox2的高迁移率族框中产生了六个取代。一个突变体在Fgf4增强子上显示出降低的DNA弯曲活性（46度而非80度），与野生型蛋白相比，这导致了更强的反式激活。然后我们在Fgf4增强子中选择了两个单碱基突变，这些突变使DNA更不易被Sox2蛋白弯曲。同样，不同的DNA弯曲角度（0度和42度而非80度）导致了不同的转录激活，但在这种情况下，弯曲减少对应于转录减少。我们发现，相似DNA弯曲角度对转录的相反影响是由于DNA弯曲的相对取向存在20度差异，这证明增强体复合物正确的三维几何结构对于促进转录是必要的。
