DNA Supercoiling- Fundamental Feature of DNA Topology
DNA topology refers to the shape and spatial arrangement of DNA molecules. Because DNA is a
double helix, its structure can become complex, especially when it's circular or constrained
within a cell. DNA topology examines how the two strands of the DNA double helix are
intertwined and how this intertwining affects the molecule's three-dimensional shape.
Topological characteristics of DNA and specifically DNA supercoiling influence all major DNA
transactions in living cells. DNA supercoiling induces the formation of unusual secondary
structure by specific DNA repeats which can also affect DNA functioning
Topological aspects of DNA structure arise primarily from the fact that the two DNA strands are
repeatedly intertwined. They involve supercoiling, knotting, and catenation (linking of rings).
Supercoiling
Supercoiling refers to the over- or under-winding of helically coiled DNA around its axis thus
trapping or releasing the free energy stored in the molecule; winding in the same direction as the
helix introduces positive supercoiling whereas winding in the opposite direction generates
negative supercoiling.
It is a fundamental property of DNA and chromatin. It is modulated by polymerase and
topoisomerase activities and, through regulated constraint, by DNA/chromatin binding proteins.
In prokaryotes and eukaryotes all activities that require DNA to be unwound (and rewound) are
potent generators of supercoiling. The classic example is the ‘twin supercoiled domain’ model
where elongating RNA polymerase, in unwinding the DNA, generates positive supercoiling
ahead and, in rewinding the DNA, generates negative supercoiling in its wake [7,8] (Figure 1).
The levels of supercoiling produced in this process are prodigious, amounting to a positive and a
negative supercoil for every 10 bp transcribed.
DNA topology refers to the shape and spatial arrangement of DNA molecules. Because DNA is a
double helix, its structure can become complex, especially when it's circular or constrained
within a cell. DNA topology examines how the two strands of the DNA double helix are
intertwined and how this intertwining affects the molecule's three-dimensional shape.
Topological characteristics of DNA and specifically DNA supercoiling influence all major DNA
transactions in living cells. DNA supercoiling induces the formation of unusual secondary
structure by specific DNA repeats which can also affect DNA functioning
Topological aspects of DNA structure arise primarily from the fact that the two DNA strands are
repeatedly intertwined. They involve supercoiling, knotting, and catenation (linking of rings).
Supercoiling
Supercoiling refers to the over- or under-winding of helically coiled DNA around its axis thus
trapping or releasing the free energy stored in the molecule; winding in the same direction as the
helix introduces positive supercoiling whereas winding in the opposite direction generates
negative supercoiling.
It is a fundamental property of DNA and chromatin. It is modulated by polymerase and
topoisomerase activities and, through regulated constraint, by DNA/chromatin binding proteins.
In prokaryotes and eukaryotes all activities that require DNA to be unwound (and rewound) are
potent generators of supercoiling. The classic example is the ‘twin supercoiled domain’ model
where elongating RNA polymerase, in unwinding the DNA, generates positive supercoiling
ahead and, in rewinding the DNA, generates negative supercoiling in its wake [7,8] (Figure 1).
The levels of supercoiling produced in this process are prodigious, amounting to a positive and a
negative supercoil for every 10 bp transcribed.
