Faculty of Life and Medical Sciences, Doshisha University, Kyoto, Japan.
College of Life Sciences, Ritsumeikan University, Shiga, Japan.
PLoS One. 2018 Mar 1;13(3):e0193595. doi: 10.1371/journal.pone.0193595. eCollection 2018.
Polyamines have various biological functions including marked effects on the structure and function of genomic DNA molecules. Changes in the higher-order structure of DNA caused by polyamines are expected to be closely related to genetic activity. To clarify this issue, we examined the relationship between gene expression and the higher-order structure of DNA under different polyamine concentrations.
We studied the effects of polyamines, spermidine SPD(3+) and spermine SP(4+), on gene expression by a luciferase assay. The results showed that gene expression is increased by ca. 5-fold by the addition of SPD(3+) at 0.3 mM, whereas it is completely inhibited above 2 mM. Similarly, with SP(4+), gene expression is maximized at 0.08 mM and completely inhibited above 0.6 mM. We also performed atomic force microscopy (AFM) observations on DNA under different polyamine concentrations. AFM revealed that a flower-like conformation is generated at polyamine concentrations associated with maximum expression as measured by the luciferase assay. On the other hand, DNA molecules exhibit a folded compact conformation at polyamine concentrations associated with the complete inhibition of expression. Based on these results, we discuss the plausible mechanism of the opposite effect, i.e., enhancement and inhibition, of polyamines on gene expression.
It was found that polyamines exert opposite effect, enhancement and inhibition, on gene expression depending on their concentrations. Such an opposite effect is argued in relation to the conformational change of DNA: enhancement is due to the parallel ordering of DNA segments that is accompanied by a decrease in the negative charge of double-stranded DNA, and inhibition is caused by the compaction of DNA into a tightly packed state with almost perfect charge-neutralization.
多胺具有多种生物学功能，包括对基因组 DNA 分子结构和功能的显著影响。多胺引起的 DNA 高级结构的变化预计与遗传活性密切相关。为了阐明这个问题，我们研究了不同多胺浓度下基因表达与 DNA 高级结构之间的关系。
我们通过荧光素酶测定研究了多胺，即亚精胺 SPD(3+)和精胺 SP(4+)对基因表达的影响。结果表明，添加 0.3mM 的 SPD(3+)可使基因表达增加约 5 倍，而超过 2mM 时则完全抑制。同样，对于 SP(4+)，在 0.08mM 时基因表达最大，而在 0.6mM 以上时完全抑制。我们还在不同多胺浓度下对 DNA 进行了原子力显微镜 (AFM) 观察。AFM 显示，在与荧光素酶测定中最大表达相对应的多胺浓度下，生成花状构象。另一方面，在与表达完全抑制相对应的多胺浓度下，DNA 分子呈现折叠紧凑的构象。基于这些结果，我们讨论了多胺对基因表达产生相反效应，即增强和抑制的可能机制。
发现多胺对基因表达具有增强和抑制的相反作用，这取决于它们的浓度。这种相反的效应与 DNA 的构象变化有关：增强是由于 DNA 片段的平行排序，伴随着双链 DNA 负电荷的减少，而抑制是由于 DNA 紧密包装成几乎完美电荷中和的紧密状态。
