KINETICS OF THE SALT-INDUCED B-DNA TO Z-DNA TRANSITION

The salt-induced B- to Z-DNA conformational transition is a cooperativ e- and time-dependent process. From a modified form of the logistic eq uation which describes an equilibrium between two states we have deduc ed a kinetic function to quantify the degree of the B to Z transition of a synthetic (dG-dC) (dG-dC) polynucleotide. This function was obtai ned 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, c haracteristic of the type of salt used. This constant is defined as th e salt concentration needed to reach the B-Z transition-midpoint in th e time unit. The equation fits the data obtained by circular dichroism (CD) for changes in molecular ellipticity of poly(dG-m(5)dC) . poly(d G-m(5)dC) and poly(dG-dC) . poly(dG-dC) incubated with various concent rations of mono-, di-, and trivalent salts at a constant temperature. The derived expression may be a very useful tool for studying the kine tics of the B- to Z-DN;I transition.