Cation- and sequence length-dependent kinetics for B-/Z-DNA transition.

This work examined the kinetics for the B→Z-DNA transition of tandem d(CG) repeat sequences induced by NaCl, KCl, MgCl2, and spermine. While d(CG)3 undergoes an incomplete transition, d(CG)6, d(CG)9, and d(CG)18 transition fully in appropriate concentrations of salts or spermine. The transition proceeds more slowly with increasing DNA lengths. Furthermore, d(CG)18 displays complex behavior in the presence of MgCl2. While d(CG)18 fully transitions to Z-DNA in the presence of 2.5 M MgCl2, the process is complicated, likely by condensation. Kinetics of the B-/Z-DNA transition is an important aspect of Z-DNA's roles in biological systems. The knowledge of how this transition is affected by sequence lengths and salts helps define the DNA's conformational plasticity in response to environmental shifts in cells.