Specific binding of lac repressor to linear versus circular polyoperator molecules.
Specific binding of lac repressor to linear versus circular polyoperator molecules.
复制标题
lac 阻遏物与线性和环状多操作分子的特异性结合。
DOI：
10.1021/bi00490a020
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发表时间：
1990
期刊：
影响因子：
2.9
通讯作者：
Betz,JL
中科院分区：
文献类型：
--
作者：
Sasmor,HM;Betz,JL
Department of Biochemistry, Biophysics and Genetics, University of Colorado School of Medicine, Denver, Colorado 80262 Received November 9, 1989; Revised Manuscript Received May 31, 1990 abstract: Gel shift assays were used to examine the binding of the lactose (lac) repressor to polyoperator DNA molecules. Specific binding was differentiated from nonspecific DNA association by (i) equilibrating repressor-operator complexes below the nonspecific association constant and (ii) demonstrating the effects of the inducer isopropyl/3-D-thiogalactoside (IPTG) on the formation of repressor-operator complexes. With the linear polyoperator molecules, all eight operator sites could be simultaneously bound by distinct repressors. However, withcircular molecules, the eight operator sites were saturable by repressor only in the nicked circular state and not in the covalently closed circular form. Under the experimental conditions used, there was no evidence of bifunctional repressor binding or loop formation. Theresults suggest that the con-formational perturbation ofDNA that occurs upon specific repressor binding was retained in topologically closed molecules and could modify other operator sites so as to make them unavailable for specific binding.Because many regulatory proteins have been reported to induce structural distortions in their target DNA sequences, such as bending, untwisting, or looping (Kotlarz et al., 1986; Dunn et al., 1984; Hatfull et al., 1987; Koudelka et al., 1988), one determinant of protein-DNA interactions may be local conformation. The lac repressor-operator system has long been a paradigm for investigation of sequence-specific inter-actions that regulate initiation of transcription, lac repressor is known to bind tighter to supercoiled DNA than to relaxed circular DNA (Wang et al., 1974; Sadler et al., 1977; Whitson et al., 1987). Additionally, specific binding is characterized by a conformational change of the operator DNA, a result of either helix unwinding, DNA bending, or a combination of
