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SynopsisWe have studied the electrical conductivity of NaDNA solutions under "saltfree" conditions a t temperatures well below the melting point of DNA, using radio-frequency dielectric and noise measurements. A conductivity discontinuity is observed at a temperature well below that a t which the usual denaturation processes and trans conformation may commence. The radio-frequency permittivity also exhibits a discontinuity a t the same temperature. For the premelting phase, the conductivity versus temperature curves consist of two linear regions with a change in slope occurring a t 23OC. This effect is related to the behavior of the ionic sheath covering the DNA macromolecule. The activation energy of the alternative current conductivity as well as that the equivalent noise conductivity results as 3.11 kcal/mole below and 4.08 kcal/mole.

Interaction between Na-DNA and the oligopeptide lysine-tyrosine-lysine (LTL) is studied by a dielectric method. The comparison between conductivities (at the frequence of 5MHz) of LTL alone and of the complex LTL-DNA allows us to show up an electrostatic interaction between LTL and phosphates sites of DNA. During the formation of the complex LTL-DNA, a certain fraction of Na+ counter-ions is ejected from the phosphates sites.

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