Faculty of Life and Medical Sciences, Doshisha University, Kyoto, Japan.
Faculty of Science and Engineering, Doshisha University, Kyoto, Japan.
PLoS One. 2020 Sep 3;15(9):e0238447. doi: 10.1371/journal.pone.0238447. eCollection 2020.
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+.
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+. 1H 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.
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.
多胺参与多种生物过程，包括对 DNA 结构和功能的显著影响。在研究多胺与 DNA 的相互作用时，我们发现多胺存在时 K+比 Na+更能增强体外基因表达。因此，我们试图阐明 K+和 Na+对基因表达影响的显著差异背后的物理化学机制。
通过细胞提取物的荧光素酶测定进行的体外实验发现，K+比 Na+更能增强 spermidine（SPD，3+）存在时的基因表达。荧光显微镜下的单链 DNA 观察表明，Na+比 K+更能强烈地阻止 DNA 折叠成紧凑状态的转变。1H NMR 测量显示，Na+比 K+更能抑制 SPD 与 DNA 的结合。因此，在富含 K+的介质中，SPD 与 DNA 的结合更有利，这通过降低负电荷有利于 RNA 聚合酶与 DNA 接触。
我们发现，Na+和 K+通过与阳离子多胺 SPD 的竞争结合对 DNA 表现出明显不同的影响，这导致基因组 DNA 的高级结构有很大差异。可以得出结论，本研究中观察到的 Na+比 K+更有利于体外基因表达的更大有利影响，很好地归因于 Na+和 K+在诱导 DNA 构象转变的竞争结合上的显著差异。
