Productive splicing of human precursor messenger RNAs (pre-mRNAs) requires the correct selection of authentic splice sites (SS) from the large pool of potential SS. Although SS consensus sequence and splicing regulatory proteins are known to influence SS usage, the mechanisms ensuring the effective suppression of cryptic SS are insufficiently explored. Here, we find that many aberrant exonic SS are efficiently silenced by the exon junction complex (EJC), a multi-protein complex that is deposited on spliced mRNA near the exon-exon junction. Upon depletion of EJC proteins, cryptic SS are de-repressed, leading to the mis-splicing of a broad set of mRNAs. Mechanistically, the EJC-mediated recruitment of the splicing regulator RNPS1 inhibits cryptic 5′SS usage, while the deposition of the EJC core directly masks reconstituted 3′SS, thereby precluding transcript disintegration. Thus, the EJC protects the transcriptome of mammalian cells from inadvertent loss of exonic sequences and safeguards the expression of intact, full-length mRNAs.

人类前体信使RNA（pre-mRNA）的生产性拼接需要从大量潜在的SS中正确选择真实的拼接位点（SS）。尽管已知SS共有序列和剪接调节蛋白会影响SS的使用，但仍未充分探索确保有效抑制隐性SS的机制。在这里，我们发现许多异常外显子SS被外显子连接复合物（EJC）有效地沉默，外显子连接复合物是沉积在外显子-外显子连接附近的剪接mRNA上的多蛋白复合物。耗尽EJC蛋白后，隐性SS受到抑制，从而导致大量mRNA的错接。从机理上讲，EJC介导的剪接调节剂RNPS1的募集抑制了5'SS的隐秘使用，而EJC核心的沉积直接掩盖了重组的3'SS，从而避免了转录本的解体。因此，EJC保护哺乳动物细胞的转录组免受外显子序列的意外丢失，并保护完整的全长mRNA的表达。