Porter S C, North A K, Wedel A B, Kustu S
Department of Plant Biology, University of California, Berkeley 94720.
Genes Dev. 1993 Nov;7(11):2258-73. doi: 10.1101/gad.7.11.2258.
To activate transcription of the glnA gene, the dimeric NTRC protein (nitrogen regulatory protein C) of enteric bacteria binds to an enhancer located approximately 100 bp upstream of the promoter. The enhancer is composed of two binding sites for NTRC that are three turns of the DNA helix apart. One role of the enhancer is to tether NTRC in high local concentration near the promoter to allow for its frequent interaction with sigma 54 holoenzyme by DNA looping. We have found that a second role of the enhancer is to ensure oligomerization of NTRC into a complex of at least two dimers that is required for transcriptional activation. Formation of this complex is greatly facilitated by a protein-protein interaction between NTRC dimers that is increased when the protein is phosphorylated.
为了激活谷氨酰胺合成酶基因（glnA）的转录，肠道细菌的二聚体NTRC蛋白（氮调节蛋白C）会结合到启动子上游约100个碱基对处的一个增强子上。该增强子由两个NTRC结合位点组成，它们相隔DNA螺旋的三圈。增强子的一个作用是将NTRC以高局部浓度束缚在启动子附近，以便通过DNA环化使其与σ54全酶频繁相互作用。我们发现增强子的第二个作用是确保NTRC寡聚化形成至少两个二聚体的复合物，这是转录激活所必需的。当该蛋白被磷酸化时，NTRC二聚体之间的蛋白质-蛋白质相互作用增强，极大地促进了这种复合物的形成。
