title: Ultrapolymorphic DNA: B, A, Z, and Z* conformations of poly(dA-dC).poly(dG-dT).
abstract: The synthetic polynucleotide poly(dA-dC).poly(dG-dT) at low ionic strength is shown to undergo conformational changes in the presence of [tris(2-aminoethyl)amine]zinc(II) chloride (ZnN4). At 100 microM ZnN4, circular dichroism and 31P NMR spectra show the formation of Z DNA. With an increase of the concentration up to 600 microM, an A-like form is obtained, and at still higher concentration, the polynucleotide reverts to the original B form. Experiments on polynucleotide samples in which some sequence errors were observed showed that spermine was necessary as well as ZnN4 to induce the Z form. At higher concentrations of spermine and ZnN4, a second Z form (Z*) is observed. Raising the ionic strength inhibits the formation of the Z form, whereas the presence of ethylene glycol favors it.
mesh_terms: D002942:Circular Dichroism; D004247:DNA; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides
chemical_list: D011089:Polydeoxyribonucleotides; C028333:poly(d(A-C).d(G-T)); D004247:DNA