Dwyer Katherine, Agarwal Neha, Gega Alisa, Ansari Athar
Department of Biological Science, Wayne State University, Detroit, MI, United States.
Front Mol Biosci. 2021 Jul 5;8:712639. doi: 10.3389/fmolb.2021.712639. eCollection 2021.
An evolutionarily conserved feature of introns is their ability to enhance expression of genes that harbor them. Introns have been shown to regulate gene expression at the transcription and post-transcription level. The general perception is that a promoter-proximal intron is most efficient in enhancing gene expression and the effect diminishes with the increase in distance from the promoter. Here we show that the intron regains its positive influence on gene expression when in proximity to the terminator. We inserted intron into different positions within and genes. Transcription Run-On (TRO) analysis revealed that the transcription of both and was maximal in constructs with a promoter-proximal intron and decreased with the increase in distance of the intron from the promoter. However, activation was partially restored when the intron was placed close to the terminator. We previously demonstrated that the promoter-proximal intron stimulates transcription by affecting promoter directionality through gene looping-mediated recruitment of termination factors in the vicinity of the promoter region. Here we show that the terminator-proximal intron also enhances promoter directionality and results in compact gene architecture with the promoter and terminator regions in close physical proximity. Furthermore, we show that both the promoter and terminator-proximal introns facilitate assembly or stabilization of the preinitiation complex (PIC) on the promoter. On the basis of these findings, we propose that proximity to both the promoter and the terminator regions affects the transcription regulatory potential of an intron, and the terminator-proximal intron enhances transcription by affecting both the assembly of preinitiation complex and promoter directionality.
内含子的一个进化保守特征是它们能够增强含有它们的基因的表达。内含子已被证明在转录和转录后水平上调节基因表达。一般的看法是，启动子近端的内含子在增强基因表达方面最有效，并且随着与启动子距离的增加，这种作用会减弱。在这里，我们表明，当内含子靠近终止子时，它会重新获得对基因表达的积极影响。我们将内含子插入到基因和基因内的不同位置。转录延伸分析（TRO）显示，在含有启动子近端内含子的构建体中，基因和基因的转录都是最大的，并且随着内含子与启动子距离的增加而降低。然而，当内含子靠近终止子时，激活作用部分恢复。我们之前证明，启动子近端内含子通过基因环化介导在启动子区域附近募集终止因子来影响启动子方向性，从而刺激转录。在这里，我们表明，靠近终止子的内含子也增强启动子方向性，并导致基因结构紧凑，启动子和终止子区域在物理上紧密相邻。此外，我们表明，启动子近端和终止子近端的内含子都有助于在启动子上组装或稳定前起始复合物（PIC）。基于这些发现，我们提出，靠近启动子和终止子区域都会影响内含子的转录调控潜力，并且靠近终止子的内含子通过影响前起始复合物的组装和启动子方向性来增强转录。
