Polyamine-induced B-DNA to Z-DNA conformational transition of a plasmid DNA with (dG-dC)(n) insert

T. J. Thomas, U. B. Gunnia, T. Thomas

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We investigated the ability of natural polyamines putrescine, spermidine, and spermine to provoke a left-handed Z-DNA conformation in a recombinant plasmid (pDHg16) with a 23-base pair insert of (dG-dC)(n)·(dG-dC)(n) sequences. Using a monoclonal anti-Z-DNA antibody (Z22) and an enzyme-linked immunosorbent assay protocol, we found that spermidine and spermine were capable of converting pDHg16 to the Z-DNA form. The concentrations of spermidine and spermine at the midpoint of the B-DNA to Z-DNA transition were 280 and 5 μM, respectively, in buffer containing 50 mM NaCl, 1 mM sodium cacodylate, and 0.15 mM EDTA, pH 7.4. A plot of ln[Na+] versus ln [spermine4+], where [Na+] is the bulk NaCl concentration and [spermine4+] is the spermine concentration at the midpoint of the B-DNA to Z-DNA transition, gave a straight line with a slope of 1.2. Structural specificity was clearly evident in the efficacy of three spermidine homologs to induce the Z-DNA conformation in pDHg16. Putrescine and acetylspermidines had no effect on the conformation of the plasmid DNA up to a 3 mM concentration. Control experiments with the parental plasmid (pDPL6) showed no binding of the plasmid DNA with Z22. These results indicate that spermidine and spermine are capable of provoking the left-handed Z-DNA conformation in small blocks of (dG-dC)(n) sequences embedded in a right-handed B-DNA matrix. Since blocks of (dG-dC)(n) sequences are found in certain native DNAs, conformational alterations of these regions to the Z-DNA form in the presence of polyamines may have important gene regulatory effects.

Original languageEnglish (US)
Pages (from-to)6137-6141
Number of pages5
JournalJournal of Biological Chemistry
Issue number10
StatePublished - 1991

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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