He Y Y, Stockley P G, Gold L
Department of Molecular Cellular and Developmental Biology, University of Colorado at Boulder 80309, USA.
J Mol Biol. 1996 Jan 12;255(1):55-66. doi: 10.1006/jmbi.1996.0006.
The SELEX procedure was used to study the recognition between the E. coli methionine repressor (MetJ) and its DNA binding sites. DNA ligands with high affinity for either the holo-repressor or apo-repressor were isolated from a pool of molecules randomized over 20 base-pairs. Among 90 DNA ligands selected by holo-repressor binding, roughly 90% contain variations of two tandem, perfect eight base-pair Met-boxes, which are the consensus deduced from natural met operators. Base-pairs that are important, for specific interactions with the protein are highly conserved. The data also reveal the importance of the non-contacted operator base-pairs in facilitating the conformational changes in the operator which must occur for repressor binding. There are also effects due to the sequences of the base-pairs immediately flanking the operator site. DNA ligands selected by apo-repressor share a very similar, but not identical, consensus with that selected by holo-repressor, suggesting that the corepressor does not greatly alter the specificity of repressor binding.
利用指数富集的配体系统进化（SELEX）程序研究了大肠杆菌甲硫氨酸阻遏物（MetJ）与其DNA结合位点之间的识别作用。从一个20个碱基对随机化的分子库中分离出对全阻遏物或脱辅基阻遏物具有高亲和力的DNA配体。在通过全阻遏物结合选择出的90个DNA配体中，约90%含有两个串联的、完美的八个碱基对的Met-box变体，这是从天然甲硫氨酸操纵子推导出来的共有序列。对于与蛋白质的特异性相互作用重要的碱基对高度保守。数据还揭示了非接触的操纵基因碱基对在促进操纵基因构象变化中的重要性，而这种构象变化是阻遏物结合所必需的。紧邻操纵基因位点的碱基对序列也有影响。脱辅基阻遏物选择的DNA配体与全阻遏物选择的DNA配体具有非常相似但不完全相同的共有序列，这表明辅阻遏物不会极大地改变阻遏物结合的特异性。
