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Dynamic Structure of Z-DNA

1983; Springer Nature (Netherlands); Linguagem: Inglês

10.1007/978-94-009-7225-4_4

0924-4875

M. Leng, Brigitte Hartmann, Bernard Malfoy, J. Pilet, Marius Ptak,

RNA and protein synthesis mechanisms

We first show that under topological constraints segments of natural DNA containing (A.T) and (G.C) base pairs can adopt the Z conformation. This is deduced from the titration of form V DNA by the antibodies to Z-DNA. We then report some results on exchange kinetics of the protons involved in hydrogen bonds between base pairs of poly(dG-m5dC).poly(dG-m5dC), in Z conformation. There are two classes of protons, a fast one the exchange half-time of which is 40 mn and a slow one the exchange half-time of which is 960 mn. These values are deduced from infrared absorption measurements in 2H2O and H2O. These half-times are in good agreement with those determined for several alternating polynucleotides in Z-form and confirm the difference between the dynamic structure of B and Z-forms. Finally, we have studied the thermal stability of (m5dC-dG)3 by 31P nuclear magnetic resonance, circular dichroism and ultra-violet absorption. In 3 M NaC1O4, (m5dC-dG)3 has the Z conformation. The melting curve of the hexanucleotide is biphasic. The first transition occurs over a large range of temperature. It corresponds to a conformational change due to an intramolecular non-cooperative process. This new conformation is not the B-form. The second transition is cooperative and corresponds to the melting of a double helix into single strands.