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Illustration of how cold shock affects the supercoiling state of the DNA, by blocking the activity of Gyrase. The signs ' − ' and '+' represent negative and positive supercoiling, respectively. Created with BioRender.com. Also shown is a stochastic model of gene expression during cold shock as a function of the global DNA supercoiling state.
Reverse gyrase is a type I topoisomerase that introduces positive supercoils into DNA, [1] contrary to the typical negative supercoils introduced by the type II topoisomerase DNA gyrase. These positive supercoils can be introduced to DNA that is either negatively supercoiled or fully relaxed. [ 2 ]
Transcription by RNA polymerase also generates positive supercoiling ahead of, and negative supercoiling behind, the transcriptional complex (Fig. 2). This effect is known as the twin-supercoiled domain model, as described by Leroy Liu and James Wang in 1987. [21]
DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases [1] that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-polymerase [2] or by helicase in front of the progressing replication fork.
The enzyme uses the hydrolysis of ATP to introduce positive supercoils and overwinds DNA, a feature attractive in hyperthermophiles, in which reverse gyrase is known to exist. Rodriguez and Stock have done further work to identify a "latch" that is involved in communicating the hydrolysis of ATP to the introduction of positive supercoils.
DNA gyrase introduces negative supercoiling in the presence of ATP and it removes positive supercoiling in the absence of ATP. [99] Across all forms of life, DNA gyrase is the only topoisomerase that can create negative supercoiling and it is because of this unique ability that bacterial genomes possess free negative supercoils; DNA gyrase is ...
While topoisomerase IV does relax positive supercoils like DNA gyrase, it does not introduce further negative supercoiling like the latter enzyme. [ 1 ] Topoisomerase IV can unknot right-handed knots and decatenate right-handed catenanes without acting on right-handed plectonemes in negatively supercoiled DNA molecules, based on geometrical ...
A plasmid is tightly wound into a negative supercoil (a). To release the intersecting states, the torsional energy must be released by utilizing nicks (b). After introducing a nick in the system, the negative supercoil gradually unwinds (c) until it reaches its final, circular, plasmid state (d). [2]