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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.
Type II topoisomerases increase or decrease the linking number of a DNA loop by 2 units, and it promotes chromosome disentanglement. For example, DNA gyrase, a type II topoisomerase observed in E. coli and most other prokaryotes, introduces negative supercoils and decreases the linking number by 2.
The diagram shows the effects of nicks on intersecting DNA in a twisted plasmid. Nicking can be used to dissipate the energy held up by intersecting states. The nicks allow the DNA to take on a circular shape. [2] The diagram shows the effects of nicks on intersecting DNA forms. A plasmid is tightly wound into a negative supercoil (a).
With DNA in its "relaxed" state, a strand usually circles the axis of the double helix once every 10.4 base pairs, but if the DNA is twisted the strands become more tightly or more loosely wound. [43] If the DNA is twisted in the direction of the helix, this is positive supercoiling, and the bases are held more tightly together.
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 found in all bacteria but absent from higher eukaryotes. In contrast, Topo I opposes DNA gyrase by relaxing the negatively ...
Negative supercoils favor local unwinding of the DNA, allowing processes such as transcription, DNA replication, and recombination. Negative supercoiling is also thought to favour the transition between B-DNA and Z-DNA , and moderate the interactions of DNA binding proteins involved in gene regulation .
DNA in cells is negatively supercoiled and has the tendency to unwind. Hence the separation of strands is easier in negatively supercoiled DNA than in relaxed DNA. The two components of supercoiled DNA are solenoid and plectonemic. The plectonemic supercoil is found in prokaryotes, while the solenoidal supercoiling is mostly seen in eukaryotes.
The packaging of eukaryotic DNA into chromatin is a barrier to all DNA-based processes that require enzyme action. For most DNA repair processes, the chromatin must be remodeled . In eukaryotes, ATP -dependent chromatin remodeling complexes and histone-modifying enzymes are two factors that act to accomplish this remodeling process after DNA ...