Z form of poly d(A-T).poly d(A-T) in solution studied by CD and UV spectroscopies.

Near UV CD spectra, UV absorption spectra and their first derivatives have been recorded on poly d(A-T).poly d(A-T) solutions in presence of high NaCl concentration and various amounts of NiCl2. Comparison of the results presented here with those obtained for poly d(G-C).poly d(G-C) and poly d(A-C).poly d(G-T) in comparable conditions, and the I.R. and Raman data on poly d(A-T).poly d(A-T), allows us to assign the new spectra to the Z conformation of poly d(A-T).poly d(A-T) in solution. The mechanism by which nickel ions induce the B----Z interconversion in the presence of high NaCl concentration is discussed.

Spectroscopic studies of conformational transitions in double stranded DNAs in the presence of carcinogenic nickel compounds and an antitumoral drug (SOAZ).

The influence of an antitumoral drug, the pentaziridinocyclodiphosphatiazene (SOAZ), on the right----left-handed helix conformational transition of Poly (dG-dC). Poly (dG-dC) induced by carcinogenic or mutagenic Nickel compounds has been studied by ultraviolet absorbance and circular dichroïsm measurements. The B----Z transition of the polynucleotide is induced in two steps, in a similar way whatever the origin of the Nickel ions (NiCl2, NiSO4, Ni3S2, NiCO3). The midpoint of the second step (right----left-transition) is located around 0.4 mM Ni2+. The addition of SOAZ to the Poly (dG-dC). Poly (dG-dC) modifies this transition which is shifted to 2 mM Ni2+ for a 1 SOAZ/10 DNA phosphates ratio. The right-handed helix is stabilized and for a 1.5 SOAZ/phosphate ratio no B----Z transition is observed even for a tenfold amount of added Nickel (4 mM Ni2+). The addition of SOAZ to the DNA initially converted to a Z conformation by the presence of Nickel inhibits the return to the B form.

Z-form induction in DNA by carcinogenic nickel compounds: an optical spectroscopy study.

The B----Z conformational transition of double-stranded poly(dG-dC) induced by various nickel salts (chloride, sulfate, subsulfide, carbonate) has been studied by ultraviolet absorption and circular dichroism. The spectra of the nickel compounds, both free and complexed with DNA, have been obtained in the visible and near infrared regions. In all cases the nickel adopts the hexacoordinated ionic form [Ni(H2O6]2+ and induces the B----Z transition of the nucleic acid at submillimolar concentrations (typically 0.4 mM). The addition to the poly(dG-dC)-poly(dG-dC) of an antitumoral drug, pentaziridinocyclodiphosphathiazene (SOAz), inhibits the B----Z transition even at a ten-fold higher nickel concentration (4 mM). Possible implications for carcinogenesis are discussed.