Kinetics of the salt-induced B- to Z-DNA transition

Abstract

The salt-induced B- to Z-DNA conformational transition is a cooperative- and time-dependent process. From a modified form of the logistic equation which describes an equilibrium between two states we have deduced a kinetic function to quantify the degree of the B to Z transition of a synthetic (dG-dC) ⋅ (dG-dC) polynucleotide. This function was obtained by introduction of time as a variable in the logistic function so that the equilibrium constant, K, is replaced by a new constant K _s , characteristic of the type of salt used. This constant is defined as the salt concentration needed to reach the B-Z transition-midpoint in the time unit. The equation fits the data obtained by circular dichroism (CD) for changes in molecular ellipticity of poly(dG-m⁵dC) ⋅ poly(dG-m⁵dC) and poly(dG-dC) ⋅ poly(dG-dC) incubated with various concentrations of mono-, di-, and trivalent salts at a constant temperature. The derived expression may be a very useful tool for studying the kinetics of the B- to Z-DNA transition.