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Effect of superhelical structure on the secondary structure of DNA rings

✍ Scribed by Daniel Glaubiger; John E. Hearst

Publisher
Wiley (John Wiley & Sons)
Year
1967
Tongue
English
Weight
237 KB
Volume
5
Category
Article
ISSN
0006-3525

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✦ Synopsis

Synopsis

A quantity, called the linking number, is defined, which specifies the total number of t,wists in a circular helix. The linking number is invariant under continuous deformations of the ring and therefore enables one to calculate the influence of superhelical structures on the secondary helix of a circular molecule. The linking number can be determined by projecting the helix into a plane and counting strand crosses in the projection as described. For example, it has been shown that for each 180" twist in a left-handed superhelix, a right-handed 360" twist is removed from the secondary helix, thus allowing local unwinding.

* It is also related, under an appropriate projection, to the winding number of the closed curve formed by the projected helix aboiit the point corresponding to the helix axis.

Winding number is defined as in Ahlfora,2 p. 93.

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