Abstract
Microarray analysis shows that transcription of 306 E. Coli genes is affected by changes in the level of chromosome supercoiling, suggesting that supercoiling transmits regulatory signals from the environment to many cellular pathways.
Highlights
The chromosome of Escherichia coli is maintained in a negatively supercoiled state, and supercoiling levels are affected by growth phase and a variety of environmental stimuli
In E. coli, supercoiling is maintained at a precise range during log phase growth by the topoisomerases DNA gyrase, topoisomerase I, and topoisomerase IV [5,6,7]
If supercoiling is used as a mechanism to sense environmental changes, we predict that genes from many functional classes would be affected by supercoiling, because environmental changes such as temperature and osmotic strength will affect many different reactions in the cell
Summary
The chromosome of Escherichia coli is maintained in a negatively supercoiled state, and supercoiling levels are affected by growth phase and a variety of environmental stimuli. DNA gyrase and topo IV are ATP-dependent type II topoisomerases that introduce negative supercoils and remove positive supercoils, respectively [8,9,10], whereas topo I is a type IA topoisomerase that removes negative supercoils [11] Together, these activities remove the topological effects of translocating proteins, such as RNA polymerase, that create (+) supercoils in front and (-) supercoils behind the moving protein [12,13]. Relaxation of the chromosome upregulates gyrA and gyrB and downregulates topA as a form of feedback control [14,15,16] This dual response indicates that (-) supercoiling can promote, as well as inhibit, gene expression. Determining which genes are supercoiling sensitive may illuminate principles of promoter activation, such as common sequence characteristics in promoters and regulation of transcription initiation [14,17,18]
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