A left-handed (Z) conformation of poly(dA-dC).poly(dG-dT) induced by polyamines.

AUTOR(ES)

Thomas, T J

RESUMO

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.

Documentos Relacionados

• Right-handed and left-handed helices of poly(dA-dC) X (dG-dT).
• Mercury-induced transitions between right-handed and putative left-handed forms of poly[d(A-T).d(A-T)] and poly[d(G-C).d(G-C)]
• A Z-like form of poly(dA-dC).poly(dG-dT) in solution?
• Vacuum UV circular dichroism is diagnostic for the left-handed Z form of poly [d(A-C).d(G-T)] and other polydeoxynucleotides.
• The high salt form of poly(dG-dC).poly(dG-dC) is left-handed Z-DNA: Raman spectra of crystals and solutions.