Existence of the C structure in poly(dA-dC).poly(dG-dT).
We show that the lithium salt of calf-thymus DNA can assume the C structure in nonoriented, hydrated gels. The transitions between the B and C structures showed little hysteresis and none of the metastable structural states which occur in oriented gels. Therefore crystal-lattice forces are not needed to stabilize the C structure. The occurrence of the alternative structures of the Li, Na and K salts of poly(dA-dC).poly(dG-dT) was measured as a function of hydration for nonoriented gels. Poly(dA-dC).poly(dG-dT).Li exists in the B structure at high hydrations and in the C structure at moderate hydrations with no A or Z structure at any hydration tested. The Na salt of poly(dA-dC).poly(dG-dT) exists in the B structure at high hydration, as mixtures of B and C at moderate hydrations and in the A structure at lower hydrations. The potassium salt behaves similarly except that mixtures of the C and A structures exist at lower hydrations. ZnCl2 and NaNO3, which promote the Z structure in duplex poly(dG-dC), promote the C structure in poly(dA-dC).poly(dG-dT). Information contained in the sequence of base pairs and not specific ionic interactions appear to determine the stability of the alternative structures of polynucleotides as hydration is changed.
Loprete
D M
DM
Department of Biochemistry and Biophysics, University of Rhode Island, Kingston 02881.
Hartman
K A
KA
D002712:Chlorides; D004247:DNA; D003903:Deuterium; D017666:Deuterium Oxide; D009566:Nitrates; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D013055:Spectrophotometry, Infrared; D014867:Water; D015032:Zinc; D017967:Zinc Compounds
D002712:Chlorides; D009566:Nitrates; D011089:Polydeoxyribonucleotides; D017967:Zinc Compounds; D014867:Water; C033927:poly(dA-dC).poly(dG-dT); C016837:zinc chloride; C031618:sodium nitrate; D004247:DNA; D003903:Deuterium; D015032:Zinc; D017666:Deuterium Oxide