Lal Avantika, Dhar Amlanjyoti, Trostel Andrei, Kouzine Fedor, Seshasayee Aswin S N, Adhya Sankar
National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, Karnataka, India.
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Nat Commun. 2016 Mar 30;7:11055. doi: 10.1038/ncomms11055.
DNA in bacterial cells primarily exists in a negatively supercoiled state. The extent of supercoiling differs between regions of the chromosome, changes in response to external conditions and regulates gene expression. Here we report the use of trimethylpsoralen intercalation to map the extent of supercoiling across the Escherichia coli chromosome during exponential and stationary growth phases. We find that stationary phase E. coli cells display a gradient of negative supercoiling, with the terminus being more negatively supercoiled than the origin of replication, and that such a gradient is absent in exponentially growing cells. This stationary phase pattern is correlated with the binding of the nucleoid-associated protein HU, and we show that it is lost in an HU deletion strain. We suggest that HU establishes higher supercoiling near the terminus of the chromosome during stationary phase, whereas during exponential growth DNA gyrase and/or transcription equalizes supercoiling across the chromosome.
细菌细胞中的DNA主要以负超螺旋状态存在。超螺旋程度在染色体区域间存在差异，会随外部条件变化而改变，并调控基因表达。在此，我们报告了利用三甲基补骨脂素嵌入法来绘制大肠杆菌染色体在指数生长期和稳定期的超螺旋程度图谱。我们发现，稳定期的大肠杆菌细胞呈现出负超螺旋梯度，染色体末端的负超螺旋程度高于复制起点，而在指数生长期的细胞中不存在这种梯度。这种稳定期模式与类核相关蛋白HU的结合相关，并且我们表明在HU缺失菌株中这种模式消失。我们认为，HU在稳定期使染色体末端附近的超螺旋程度更高，而在指数生长期，DNA促旋酶和/或转录使整个染色体的超螺旋程度趋于平衡。
