期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1977
卷号：74
期号：8
页码：3292-3296
DOI：10.1073/pnas.74.8.3292
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The nitrocellulose filter assay was used to study the interactions of wild-type (SQ) and tight-binding (QX86) lac repressors with synthetic lac operators 21 and 26 base pairs long. The repressor binding properties of both operators were very similar, indicating that both contain the same specific repressor recognition sites. The repressor-operator association rate constants (ka) were more sensitive than dissociation rate constants (kd) to changes in ionic strength. The responses of both ka and kd to ionic strength were relatively small compared to the effects previously observed with {lambda}h80dlac as operator DNA. These results suggest that under natural conditions there are electrostatic interactions between lac repressor and DNA regions outside of the 26 base pair operator sequence. Association rate constants for SQ repressor with either operator are higher than have been predicted for diffusion-limited reactions. We postulate that long-range electrostatic attractions between repressor and operator accelerate the association reaction. The presence of nonoperator DNA decreased association rate constants, the effect being more noticeable at an ionic strength of 0.05 M than at 0.20 M. Nonoperator DNA reduced ka values for associations involving QX86 repressor to a greater extent than for those with SQ repressor. The two types of repressors also had different rate constants for interactions with synthetic operators. The values for ka and kd were both higher with SQ repressor than with QX86 repressor. However, the rate constants were more sensitive to ionic strength when the repressor used was QX86.
关键词：nonoperator DNA ; salt effects ; QX86 repressor ; SQ repressor
