Concentration of polyamines (|jM)
Fig. 6. Immunological and ultraviolet spectroscopic detection of the B-DNA to Z-DNA transition of poly(dG-m5dC)-poly(dG-m5dC) in the presence of polyamines in 50 mM NaCl, 1 mM Na cacodylate, and 0.15 mMEDTA (pH 7.4). The polynucleotide was incubated with different concentrations of polyamines for 30 min and added to the microtiter plates. Enzyme immunoassay was conducted by subsequent addition of monoclonal Z-DNA antibody Z22, alkaline conjugated immunoglobulins, and the enzyme substrate as described by ref. 35. Optical density was read at 405 nm (A405 ) with a microplate autoreader. A405 nm is plotted against the concentration of AP2 (•), AP3 (▲), AP4 (spermidine) (▼), and AP5 (■) added to the polynucleotide. In ultraviolet spectroscopy, the absorbance ratio of poly(dG-m5dC)-poly(dG-m5dC) (A260/A295) was monitored at different concentrations of AP2 (o), AP3 (A), AP4 (v) and AP5 (□). (Reprinted with permission from ref. 35.)
increased the effectiveness of binding of the ICP-4, a herpes simplex virus gene regulator to its specific binding sequence on the DNA. They also found that the association constants of the transcription factor to its specific site on the DNA were increased in the presence of polyamines. The authors concluded that this increase in complex formation occurred as polyamines increased the affinity of the protein for its cognate DNA site by increasing the initial binding step. A study by Thomas and Kiang (5) demonstrated a 22-fold increase in the binding of the estrogen receptor (ER) to poly(dA-dC)/poly(dG-dT) in the presence of spermidine. In the same study, they compared the affinity of the same ER with poly(dA-dT)-poly(dA-dT) and found only a threefold increase in the presence of polyamines, suggesting a sequence-specific effect of polyamines on protein-DNA binding. The authors reasoned that this specific preference
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