Z-DNA and other non-B-DNA structures are reversed to B-DNA by interaction with netropsin

Abstract

The interaction between the B-form specific ligands netropsin (Nt) and distamycin-3 (Dst-3) and DNA duplexes has been studied under conditions of salt concentration and low water activity that modify the polymer conformation into a non-B DNA form, putatively a Z-like form. Three polymers with strict alternating purine-pyrimidine sequences and GC content from 100—0% have been tested: poly(dG—dC)·poly(dG—dC), poly(dA—dC)·poly(dG—dT) and poly(dA—dT)·poly(dA—dT). The titrations by Nt and Dst-3 were followed by circular dichroism. Although specific binding of Nt to the Z-form of poly(dG—dC)·poly(dG—dC) does not occur, Nt reverses this Z structure to the B-type conformation; Dst-3 is, however, totally inefficient. The presumed non-B or Z-like structure of poly(dA—dC)·poly(dG—dT) is reversed to the B-form upon interaction with Nt; Dst-3 also induces this reversal but at higher ligand ratios. The modified B-structure of poly(dA—dT)·poly(dA—dT) in low water activity is efficiently reversed to the B-form by interaction with both Nt and Dst-3.