K(+) promotes the favorable effect of polyamine on gene expression better than Na(+)

BACKGROUND: Polyamines are involved in a wide variety of biological processes including a marked effect on the structure and function of DNA. During our study on the interaction of polyamines with DNA, we found that K(+) enhanced in vitro gene expression in the presence of polyamine more strongly than Na(+). Thus, we sought to clarify the physico-chemical mechanism underlying this marked difference between the effects of K(+) and Na(+). PRINCIPAL FINDINGS: It was found that K(+) enhanced gene expression in the presence of spermidine, SPD(3+), much more strongly than Na(+), through in vitro experiments with a Luciferase assay on cell extracts. Single-DNA observation by fluorescence microscopy showed that Na(+) prevents the folding transition of DNA into a compact state more strongly than K(+). (1)H NMR measurement revealed that Na(+) inhibits the binding of SPD to DNA more strongly than K(+). Thus, SPD binds to DNA more favorably in K(+)-rich medium than in Na(+)-rich medium, which leads to favorable conditions for RNA polymerase to access DNA by decreasing the negative charge. CONCLUSION AND SIGNIFICANCE: We found that Na(+) and K(+) exhibit markedly different effects through competitive binding with a cationic polyamine, SPD, to DNA, which causes a large difference in the higher-order structure of genomic DNA. It is concluded that the larger favorable effect of Na(+) than K(+) on in vitro gene expression observed in this study is well attributable to the significant difference between Na(+) and K(+) on the competitive binding inducing conformational transition of DNA.