Kostrewa D, Granzin J, Koch C, Choe H W, Raghunathan S, Wolf W, Labahn J, Kahmann R, Saenger W
Institut für Kristallographie, Freie Universität Berlin, Germany.
Nature. 1991 Jan 10;349(6305):178-80. doi: 10.1038/349178a0.
The factor for inversion stimulation, FIS, is involved in several cellular processes, including site-specific recombination and transcriptional activation. In the reactions catalysed by the DNA invertases Gin, Hin and Cin, FIS stimulates recombination by binding to an enhancer sequence. Within the enhancer, two FIS dimers (each 2 x 98 amino acids) bind to two 15-base-pair consensus sequences and induce bending of the DNA. Current models propose that the enhancer-FIS complex organizes a specific synapse, either through direct interactions with Gin, or by modelling the substrate into a configuration suitable for recombination. Using X-ray analysis at 2.0 A resolution, we now show that FIS is composed of four alpha helices tightly intertwined to form a globular dimer with two protruding helix-turn-helix motifs. The 24 N-terminal amino acids are so poorly defined in the electron density map as to make interpretation doubtful, indicating that they might act as 'feelers' suitable for DNA or protein (invertase) recognition. We infer from model building that DNA has to bend for tight binding to FIS.
反向刺激因子（FIS）参与多种细胞过程，包括位点特异性重组和转录激活。在由DNA转化酶Gin、Hin和Cin催化的反应中，FIS通过与增强子序列结合来刺激重组。在增强子内，两个FIS二聚体（每个由2×98个氨基酸组成）与两个15个碱基对的共有序列结合，并诱导DNA弯曲。当前模型认为，增强子-FIS复合物通过与Gin直接相互作用，或通过将底物塑造成适合重组的构型来组织特定的突触。利用分辨率为2.0埃的X射线分析，我们现在表明FIS由四个紧密缠绕的α螺旋组成，形成一个具有两个突出的螺旋-转角-螺旋基序的球状二聚体。在电子密度图中，24个N端氨基酸的定义非常模糊，以至于难以解释，这表明它们可能作为适合DNA或蛋白质（转化酶）识别的“触角”。我们从模型构建中推断，DNA必须弯曲才能与FIS紧密结合。
