Two domains within σ(N) (σ(54)) cooperate for DNA binding

The σ-N (σ(N)) subunit of the bacterial RNA polymerase is a sequence specific DNA-binding protein. The RNA polymerase holoenzyme formed with σ(N) binds to promoters in an inactive form and only initiates transcription when activated by enhancer-binding positive control proteins. We now provide evidence to show that the DNA-binding activity of σ(N) involves two distinct domains: a C-terminal DNA-binding domain that directly contacts DNA and an adjacent domain that enhances DNA-binding activity. The sequences required for the enhancement of DNA binding can be separated from the sequences required for core RNA polymerase binding. These results provide strong evidence for communication between domains within a transcription factor, likely to be important for the function of σ(N) in enhancer-dependent transcription.

细菌RNA聚合酶的σ-N (σ(N))亚基是一种序列特异性DNA结合蛋白（sequence-specific DNA-binding protein）。由σ(N)组装形成的RNA聚合酶全酶（RNA polymerase holoenzyme）会以非活性形式结合启动子（promoter），仅在被增强子结合型正调控蛋白（enhancer-binding positive control protein）激活后才会起始转录。本研究现已提供证据表明，σ(N)的DNA结合活性包含两个截然不同的结构域：一个可直接与DNA发生接触的C端DNA结合结构域（C-terminal DNA-binding domain），以及一个毗邻该结构域、能够增强DNA结合活性的结构域。介导DNA结合增强所需的序列，可与核心RNA聚合酶（core RNA polymerase）结合所需序列相互分离。上述研究结果为转录因子（transcription factor）内部结构域间的信号通信提供了有力佐证，这一机制对于σ(N)在依赖增强子的转录过程中发挥功能或许具有重要意义。