Helical Repeats of Left-Handed DNA

Youcheng Xu

doi:10.4236/ojmip.2014.42003

Abstract

DNA is generally assumed as a right-handed double helix and Z-DNA is a special kind of left-handed DNA infrequently found in nature. However, the finding of a zero linking number topoisomer supports a hypothesis that the two strands of DNA are winding ambidextrously, rather than plectonemically. It logically leads to a notion that the left-handed DNA is as common as right-handed DNA and the amount of left-handed DNA in a positively supercoiled plasmid prevails that of the right-handed DNA. In this report, the helical repeat of left-handed DNA, 12 bp per turn, was determined by a new method. How the positively supercoiled DNA was generated in hyperthermophiles and why their DNA can withstand the extreme high temperature are answered from an alternative theory.

Highlights

Z-DNA was determined as a left-handed DNA by X-ray crystallography prior to other right-handed DNAs [1]
The finding of zero linking number topoisomer supports an alternative DNA structural hypothesis, the ambidextrous double helix, where there are a lot of left-handed DNAs coexisting with the righthanded DNA in the same native macromolecule [2]
Its accuracy is well accepted and has been applied in the field of DNA topology to substitute the old equation proposed by Vinograd some years earlier, α = β + τ [13]

Summary

Introduction

Z-DNA was determined as a left-handed DNA by X-ray crystallography prior to other right-handed DNAs [1]. It is generally believed that under physiological conditions native DNA is mainly in the form of right-handed B-DNA. The finding of zero linking number topoisomer supports an alternative DNA structural hypothesis, the ambidextrous double helix, where there are a lot of left-handed DNAs coexisting with the righthanded DNA in the same native macromolecule [2]. Such a conceptual change would have many consequences previously unimaginable. It would have an impact on the theory of DNA topology and the double helix

Methods

Results

Conclusion