Departamento de Microbiología, Universidad de Sevilla, Seville, Spain.
Gene. 2018 Jul 15;663:101-109. doi: 10.1016/j.gene.2018.04.007. Epub 2018 Apr 10.
The exon junction complex (EJC) is a key element of the splicing machinery. The EJC core is composed of eIF4A3, MAGO, Y14 and MLN51. Few accessory proteins, such as CWC22 or UPF3, bind transiently to the EJC. The EJC has been implicated in the control of the splicing of long introns. To ascertain whether the EJC controls the splicing of short introns, we used Paramecium tetraurelia as a model organism, since it has thousands of very tiny introns. To elucidate whether EJC affects intron splicing in P. tetraurelia, we searched for EJC protein-coding genes, and silenced those genes coding for eIF4A3, MAGO and CWC22. We found that P. tetraurelia likely assembles an active EJC with only three of the core proteins, since MLN51 is lacking. Silencing of eIF4A3 or CWC22 genes, but not that of MAGO, caused lethality. Silencing of the MAGO gene caused either an increase, decrease, or no change in intron retention levels of some intron-containing mRNAs used as reporters. We suggest that a fine-tuning expression of EJC genes is required for steady intron removal in P. tetraurelia. Taking into consideration our results and those published by others, we conclude that the EJC controls splicing independently of the intron size.
外显子结合复合体（EJC）是剪接机制的关键元件。EJC 核心由 eIF4A3、MAGO、Y14 和 MLN51 组成。少数辅助蛋白，如 CWC22 或 UPF3，会短暂结合到 EJC 上。EJC 被认为参与了长内含子剪接的调控。为了确定 EJC 是否控制短内含子的剪接，我们使用四膜虫作为模型生物，因为它有数千个非常小的内含子。为了阐明 EJC 是否影响四膜虫的内含子剪接，我们搜索了 EJC 蛋白编码基因，并沉默了编码 eIF4A3、MAGO 和 CWC22 的基因。我们发现，由于 MLN51 的缺失，四膜虫可能组装了一个具有三个核心蛋白的活性 EJC。沉默 eIF4A3 或 CWC22 基因，但不是 MAGO 基因，会导致细胞死亡。沉默 MAGO 基因会导致一些用作报告基因的内含子 mRNA 的内含子保留水平增加、减少或没有变化。我们认为，EJC 基因的精细表达对于四膜虫稳定的内含子去除是必需的。考虑到我们的结果和其他人的研究结果，我们得出结论，EJC 独立于内含子大小控制剪接。
