Conformational Transitions in Poly d(CGCGCGTTAATT)

Abstract

Conformational studies on poly d(CGCGCGTTAATT) in solution by circular dichroism spectroscopy are reported. The polynucleotide exhibits B conformation in sodium chloride solution and on addition of NiCl₂ a B-Z transition is observed. NiCl₂ titrations carried out in the presence of 5M NaCl show a midpoint of transition at 2.25 mM NiCl₂ and a complete (maximum conversion to Z form) transition at 16 mM NiCl₂. In 60% alcohol the polynucleotide remains in B conformation. The polynucleotide isomerizes into ψ and A conformations in the presence of spermidine and spermine respectively. The thermodynamic parameters calculated from the melting profiles using a two state model show that the polynucleotide is almost equally stable in its B and Z conformations.