Metal Ion Induced Conformational Changes of Double‐Stranded Polynucleotides: Poly (dG‐m5dC) and Poly (dA‐dT)

摘要: Like poly(dG-dC), also double-stranded poly(dG-m 5 dC) can adopt a left-handed Z-conformation. The concentrations of Ni 2+ or Mg which are required in order to induce the structural transition much lower than case unmethylated polynucleotide. At ionic strength I = 0.001 M, one ion bound per 20 mononucleotide units is sufficient trigger conformational change. kinetics binding polynucleotide characterized by reaction effect with time constant 7 - 9 milliseconds (stopped-flow and T-jump), indicating innersphere binding. kinetic data consistent 3-step mechanism includes two inner-sphere substitution processes, presumably involving phosphate 0 atom guanine N atom. slow B→Z was monitored up 1 hour. curves be fitted excellently 3 exponentials, shorter constants being dependent on concentration. A simple experimental proposed discussed. Also poly(dA-dT).poly(dA-dT) drastic change conformation after addition observed, reflecting again transition. Here, however, high (0.075-0.55 M) NaCl (0.1-5 start rate faster dC), evaluated 0.9-1.9 seconds for 0.5-0.7 M 0.1 solution.