Brenowitz M, Senear D F, Ackers G K
Department of Biology, Johns Hopkins University, Baltimore, MD 21218.
Nucleic Acids Res. 1989 May 25;17(10):3747-55. doi: 10.1093/nar/17.10.3747.
The binding of cI-repressor to a series of mutant operators containing OR1 of the right operator of bacteriophage lambda was investigated. Sites OR2 and/or OR3 were inactivated by either point or deletion mutations. The free energy of binding repressor to OR1 in the wildtype operator, delta G1, is -13.7 +/- 0.3 kcal/mol. delta G1 determined for an OR2- operator created by a single point mutation in OR2 is -13.6 +/- 0.2 kcal/mol. In contrast, delta G1 for the binding of repressor to a cloned synthetic OR1 operator containing only 24 bp of lambda sequence is -12.2 +/- 0.1 kcal/mol. When sequence 5' to OR1 is present, the binding affinity increases to -13.0 +/- 0.1 kcal/mol. In addition, the proximity of OR1 to a fragment-end decreases delta G1 from -13.7 to -12.3 +/- 0.1 kcal/mol. These results suggest that the DNA sequence outside the 17 bp OR1 binding-site contributes to the specific binding of cI-repressor.
研究了cI阻遏蛋白与一系列含有噬菌体λ右操纵子OR1的突变操纵子的结合情况。OR2和/或OR3位点通过点突变或缺失突变而失活。野生型操纵子中阻遏蛋白与OR1结合的自由能ΔG1为-13.7±0.3千卡/摩尔。由OR2中的单点突变产生的OR2-操纵子的ΔG1为-13.6±0.2千卡/摩尔。相比之下，阻遏蛋白与仅包含24个碱基对λ序列的克隆合成OR1操纵子结合的ΔG1为-12.2±0.1千卡/摩尔。当OR1 5'端的序列存在时，结合亲和力增加到-13.0±0.1千卡/摩尔。此外，OR1与片段末端的接近使ΔG1从-13.7降至-12.3±0.1千卡/摩尔。这些结果表明，17个碱基对的OR1结合位点之外的DNA序列有助于cI阻遏蛋白的特异性结合。
