Department of Microbiology and Research Institute for Translational System Biomics, Chung-Ang University College of Medicine, Seoul 156-756, Republic of Korea.
Biochem Biophys Res Commun. 2010 Jan 22;391(4):1792-7. doi: 10.1016/j.bbrc.2009.12.160. Epub 2010 Jan 5.
The gene regulation by intrinsically curved DNA is one way for bacterial sensing of and response to environmental changes. Previously, we showed that the genetic element BNT2 upstream of the ecf (eae-positive conserved fragment) operon in the Escherichia coli O157:H7 virulence plasmid (pO157) has characteristics typical of intrinsically curved DNA, including the presence of multi-homopolymeric adenine:thymine tracts (AT tracts) and electrophoretic anomaly at 4 degrees C. Here we report that a local intrinsic curvature induced by the two phased AT tracts within the unusual promoter sequence of BNT2 played a major role for its temperature-dependent promoter activity. The base substitution of the AT tract in the spacer DNA between the -35 and the unusual -10 regions of the BNT2 promoter with non-AT tract sequence reduced intrinsic curvature slightly at 4 degrees C, but greatly affected its transcriptional activity. This implies that such a local intrinsic curvature within the unusual promoter of BNT2 is important for thermoregulation of the ecf operon.
DNA 的内在弯曲对基因调控是细菌感知和响应环境变化的一种方式。此前，我们发现大肠杆菌 O157:H7 毒力质粒（pO157）上 ecf（eae 阳性保守片段）操纵子上游的遗传元件 BNT2 具有内在弯曲 DNA 的典型特征，包括多聚腺嘌呤：胸腺嘧啶（AT tracts）和在 4°C 时电泳异常。在这里，我们报告说，BNT2 不寻常启动子序列内两个相位 AT tract 引起的局部内在弯曲对其温度依赖性启动子活性起主要作用。BNT2 启动子-35 和不寻常-10 区域之间的间隔 DNA 中的 AT tract 碱基替换为非 AT 序列，在 4°C 时略微降低了内在曲率，但极大地影响了其转录活性。这意味着 BNT2 不寻常启动子内的这种局部内在曲率对于 ecf 操纵子的温度调节很重要。
