Polyamine-induced B-DNA to Z-DNA conformational transition of a plasmid DNA with (dG-dC)n insert.
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 microM, 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.
Thomas
T J
TJ
Clinical Research Center, University of Medicine and Dentistry, New Jersey-Robert Wood Johnson Medical School, New Brunswick 08903.
Gunnia
U B
UB
Thomas
T
T
D000818:Animals; D000911:Antibodies, Monoclonal; D002417:Cattle; D004247:DNA / Q000276:immunology; D004251:DNA Transposable Elements; D004797:Enzyme-Linked Immunosorbent Assay; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011073:Polyamines / Q000494:pharmacology*; D011089:Polydeoxyribonucleotides / Q000235:genetics*; D012965:Sodium Chloride
D000911:Antibodies, Monoclonal; D004251:DNA Transposable Elements; D011073:Polyamines; D011089:Polydeoxyribonucleotides; C019530:poly(dC-dG); D012965:Sodium Chloride; D004247:DNA