title: A left-handed (Z) conformation of poly(dA-dC).poly(dG-dT) induced by polyamines.
abstract: Blocks of potential Z-DNA forming alternating purine-pyrimidine (APP) sequences are widely dispersed in native DNAs. We have studied the effects of naturally occurring polyamines on the conformation of a synthetic APP sequence, poly(dA-dC).poly(dG-dT) by circular dichroism spectroscopy. In the presence of micromolar concentrations of spermidine (125 microM) and spermine (16 microM), this polymer undergoes B to Z transition in low ionic strength (2 mM Na+) buffers. The concentration of polyamines required for B to Z transition increases with Na+ in the buffer and a straight line is obtained on plotting ln[Na+] vs. ln [spermidine 3+]. However, at concentrations of polyamines higher than those necessary to induce B to Z transition, Z-DNA converts to psi-DNA, an ordered, twisted, tight packing arrangement of the double helix. These results suggest a pathway for the transient formation of Z-DNA segments in vivo by interaction of the ubiquitous polyamines with naturally occurring blocks of APP sequences.
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D011073:Polyamines; D011089:Polydeoxyribonucleotides; D011700:Putrescine; D013095:Spermidine; D013096:Spermine
chemical_list: D011073:Polyamines; D011089:Polydeoxyribonucleotides; D013096:Spermine; C033927:poly(dA-dC).poly(dG-dT); D013095:Spermidine; D011700:Putrescine