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This process occurs in bacteria, whose single circular DNA is cut by DNA gyrase and the two ends are then twisted around each other to form supercoils. Gyrase is also found in eukaryotic plastids: it has been found in the apicoplast of the malarial parasite Plasmodium falciparum [5] [6] and in chloroplasts of several plants. [7]
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).
Footprinting indicates that gyrase, which forms a 140-base-pair footprint and wraps DNA, introduces negative supercoils, while topoisomerase IV, which forms a 28-base-pair footprint, does not wrap DNA. Eukaryotic type II topoisomerase cannot introduce supercoils; it can only relax them. The roles of type IIB topoisomerases are less understood.
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 .
Where DNA gyrase forms a tetramer and is capable of cleaving a double-stranded region of DNA, reverse gyrase can only cleave single stranded DNA. [ 3 ] [ 4 ] More specifically, reverse gyrase is a member of the type IA topoisomerase class; along with the ability to relax negatively or positively supercoiled DNA [ 5 ] (which does not require ATP ...
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.
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 ...
Cruciform DNA is found in both prokaryotes and eukaryotes and has a role in DNA transcription and DNA replication, double strand repair, DNA translocation and recombination. They also serve a function in epigenetic regulation along with biological implications such as DNA supercoiling, double strand breaks, and targets for cruciform-binding ...