Institute for Evolution and Biodiversity, University of Münster, 48149, Germany.
Institute for Evolution and Biodiversity, University of Münster, 48149, Germany
G3 (Bethesda). 2017 Jul 5;7(7):2107-2114. doi: 10.1534/g3.117.041483.
In human, mouse, and , the spliceosomal complex U1 snRNP (U1) protects transcripts from premature cleavage and polyadenylation at proximal intronic polyadenylation signals (PAS). These U1-mediated effects preserve transcription integrity, and are known as telescripting. The watchtower role of U1 throughout transcription is clear. What is less clear is whether cleavage and polyadenylation factors (CPFs) are simply patrolled or if they might actively antagonize U1 recruitment. In addressing this question, we found that, in the introns of human, mouse, and , and of 14 other eukaryotes, including multi- and single-celled species, the conserved AATAAA PAS-a major target for CPFs-is selected against. This selective pressure, approximated using DNA strand asymmetry, is detected for peripheral and internal introns alike. Surprisingly, it is more pronounced within-rather than outside-the action range of telescripting, and particularly intense in the vicinity of weak 5' splice sites. Our study uncovers a novel feature of eukaryotic genes: that the AATAAA PAS is universally counter-selected in spliceosomal introns. This pattern implies that CPFs may attempt to access introns at any time during transcription. However, natural selection operates to minimize this access. By corroborating and extending previous work, our study further indicates that CPF access to intronic PASs might perturb the recruitment of U1 to the adjacent 5' splice sites. These results open the possibility that CPFs may impact the splicing process across eukaryotes.
在人类、小鼠和中，剪接体复合物 U1 snRNP（U1）保护转录本免受近端内含子多聚腺苷酸化信号（PAS）的过早切割和多聚腺苷酸化。这些 U1 介导的效应维持转录完整性，被称为转录延伸。U1 在整个转录过程中的监视作用是明确的。不太清楚的是，切割和多聚腺苷酸化因子（CPFs）是简单地巡逻，还是可能主动拮抗 U1 的募集。在解决这个问题时，我们发现，在人类、小鼠和的内含子中，以及包括多细胞和单细胞物种在内的 14 种其他真核生物的内含子中，保守的 AATAAA PAS-主要是 CPFs 的靶点-被选择。这种选择压力，使用 DNA 链不对称性来近似，可以检测到外周和内部内含子。令人惊讶的是，它在转录延伸的作用范围之内而不是之外更为明显，在弱 5' 剪接位点附近尤其强烈。我们的研究揭示了真核基因的一个新特征：AATAAA PAS 在剪接体内含子中普遍受到反选择。这种模式意味着 CPFs 可能试图在转录过程中的任何时间进入内含子。然而，自然选择会将这种进入最小化。通过证实和扩展以前的工作，我们的研究进一步表明，CPF 对内含子 PAS 的进入可能会干扰 U1 与相邻 5' 剪接位点的募集。这些结果使 CPFs 可能影响整个真核生物的剪接过程成为可能。
