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首页> 外文期刊>Journal of Molecular Biology >Modulation of Lrp action in Escherichia coli by leucine: effects on non-specific binding of Lrp to DNA.
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Modulation of Lrp action in Escherichia coli by leucine: effects on non-specific binding of Lrp to DNA.

机译：亮氨酸对大肠杆菌中Lrp作用的调节：对Lrp与DNA的非特异性结合的影响。

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摘要

Lrp is a global regulator of metabolism in Escherichia coli that helps cells respond to changes in environmental conditions. The action of Lrp as a transcriptional activator or repressor is sometimes affected by whether the medium contains exogenous leucine. The abundance of Lrp in cells is relatively high (about 15 microM in monomer), and given the relatively high Lrp binding affinity in vitro for specific binding sites (nanomolar apparent dissociation constants), the expectation is that all binding sites will be saturated with Lrp in vivo. Here we consider the fraction of the total Lrp in cells that is free and the fraction that is bound to DNA. Using minicell-producing strains, we measured the distribution of Lrp between cytoplasm and nucleoid in cells grown under different nutritional conditions and in cells in different phases of growth. In E. coli cells grown in minimal medium to mid-log phase, the ratio of free to DNA-bound Lrp was about 0.67. This ratio decreased about threefold when the cells were grown in minimal medium supplemented with leucine. Our results also confirmed the previous finding that growth rate regulates lrp expression by as much as three to fourfold. Growth rate-regulated lrp expression, along with changes in the extent of non-specific binding, influences the level of free Lrp in vivo over a 16-fold range. We propose that the net effect of these processes is to regulate the relative concentrations of free Lrp hexadecamer and leucine-bound octamer, leading to promoter selection in response to environmental conditions. Copyright 2001 Academic Press.
机译：Lrp是大肠杆菌中新陈代谢的全球调节剂，可帮助细胞响应环境条件的变化。 Lrp作为转录激活因子或阻遏因子的作用有时会受到培养基中是否含有外源亮氨酸的影响。细胞中Lrp的丰度相对较高（单体约为15 microM），并且鉴于体外对特定结合位点的Lrp结合亲和力较高（纳摩尔表观解离常数），因此预期所有结合位点都将被Lrp饱和体内。在这里，我们考虑游离的细胞中总Lrp的比例以及与DNA结合的比例。使用产生微细胞的菌株，我们测量了在不同营养条​​件下生长的细胞和处于不同生长阶段的细胞中Lrp在细胞质和核苷之间的分布。在最小培养基至对数中期的大肠杆菌细胞中，游离Lrp与结合DNA的Lrp之比约为0.67。当细胞在补充有亮氨酸的基本培养基中生长时，该比率降低了约三倍。我们的结果还证实了先前的发现，即生长速率将lrp表达调节多达三至四倍。生长速率调节的lrp表达以及非特异性结合程度的变化会在16倍范围内影响体内游离Lrp的水平。我们建议这些过程的净效应是调节游离Lrp十六烷和亮氨酸结合的八聚物的相对浓度，从而响应环境条件而选择启动子。版权所有2001学术出版社。

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