Ebright R H, Ebright Y W, Gunasekera A
Department of Chemistry, Rutgers University, New Brunswick, NJ 08855.
Nucleic Acids Res. 1989 Dec 25;17(24):10295-305. doi: 10.1093/nar/17.24.10295.
We have synthesized two 40 base pair DNA fragments; one fragment contains the consensus DNA site for CAP (fragment 'ICAP'); the other fragment contains the E. coli lac promoter DNA site for CAP (fragment 'LCAP'). We have investigated the binding of CAP to the two DNA fragments using the nitrocellulose filter binding assay. Under standard conditions [( NaCl] = 200 mM, pH = 7.3), CAP exhibits a 450-fold higher affinity for ICAP than for LCAP. The salt dependence of the binding equilibrium indicates that CAP makes eight ion pairs with ICAP, but only six ion pairs with LCAP. Approximately half of the difference in binding free energy for interaction of CAP with ICAP vs. LCAP is attributable to this difference in ion-pair formation. The pH dependence of the binding equilibrium indicates that the eight CAP-ICAP ion pairs and the six CAP-LCAP ion pairs do not involve His residues of CAP.
我们合成了两个40个碱基对的DNA片段;一个片段包含CAP的共有DNA位点(片段“ICAP”);另一个片段包含大肠杆菌乳糖启动子的CAP DNA位点(片段“LCAP”)。我们使用硝酸纤维素滤膜结合试验研究了CAP与这两个DNA片段的结合。在标准条件下([NaCl]=200 mM,pH = 7.3),CAP对ICAP的亲和力比对LCAP高450倍。结合平衡的盐依赖性表明,CAP与ICAP形成八个离子对,但与LCAP仅形成六个离子对。CAP与ICAP相互作用和与LCAP相互作用的结合自由能差异中,约一半可归因于离子对形成的这种差异。结合平衡的pH依赖性表明,八个CAP-ICAP离子对和六个CAP-LCAP离子对不涉及CAP的组氨酸残基。