Left-Handed Double Helical DNA: Variations in the Backbone Conformation

Abstract

Four different crystals of d(CpGpCpGpCpG) have been solved by x-ray diffraction analysis and all form similar left-handed double helical Z-DNA molecules in the crystal lattice. Two different conformations are observed for the phosphates in the GpC sequences, as the phosphates are found either facing the helical groove or rotated away from it. The latter conformation is often found when hydrated magnesium ions are complexed to a phosphate oxygen atom. These different conformations may be used when right-handed B-DNA joins left-handed Z-DNA. Atomic coordinates and torsion angles are presented for both types of Z-DNA.

Antiserum to Z‐DNA

“…In 1.5 M NaC104, almost all the poly(dG-dC) • poly(dG-dC) is precipitated and is not at all precipitated below 1.2 M NaC104. It is known that poly(dG-dC) • poly(dG-dC) can undergo a salt-induced conformation transition from the B-form to the Z-form [5][6][7][8][9][10]. The midpoint of the transition is at 1.8 M. In 1.2 M NaC104, only a small fraction of poly(dG-dC) • poly(dG-dC) is in Z-form.…”

“…In solution, poly-(dG-dC) • poly(dG-dC) can adopt the B-or Z-form depending upon the ionic strength of the medium [5][6][7][8][9]. Moreover, it seems possible to join sequences in B-and Z-form, respectively [ 10,11 ].…”

A → Z transition in the synthetic hexanucleotide (dCdGfl)3

“…dGfl, 2'-deoxy-2'-fluoroguanosine; NOE, nuclear Overhauser effect; CD, circular dichroism angle and sugar conformation: the deoxycytidines show anti orientation and 2'-endo puckering and the deoxyguanosines are in syn orientation with 3 ' -endo pucker [8]. This peculiar alternating arrangement is responsible for the zig-zag structure of Z-DNA.…”

Two Aspects of DNA Polymorphism and Microheterogeneity:

“…structure of Z D N A indicated that certain of its base-pair atoms on its convex face are unusually exposed, the hypothesis was put forward [1,2] that if Z-DNA segments were interspersed within a B-DNA chain, these atoms could represent privileged targets for appropriate attacking species, e.g. C-8 of guanine, C8(G), could be wch a target for the carcinogen N-2-acetylaminofluorene which preferentially attacks this site.…”

“…Two recent works seem to have had a particularly strong influence in bringing this situation to light. One is the discovery of a family of left-handed DNA double helices, termed Z DNAs, found in the crystal of the self-complementary hexamer d(C-G-C-G-C-G) [1,2] and in the high salt solution of poly(dG-dC) . poly(dG-dC) [3].…”