Pre-mRNA is transcribed with introns still in place. The spliceosome recognises splice-site consensus sequences, loops each intron into a lariat, and cuts it free while ligating the flanking exons. Alternative splicing can skip an internal exon entirely, producing a different protein isoform from the same gene.
5'-Exon1–GU...intron...AG–Exon2-3' → lariat excised → Exon1-Exon2 ligated
- Exon 2 toggle — includes or skips exon 2 during splicing (alternative splicing → a different mature mRNA/isoform).
- Cycle speed — how fast transcription, splicing, export, translation and decay proceed.
- Poly-A tail length — longer 3' poly-A tails resist deadenylation and give the mRNA a longer functional half-life (τ) before decay.
- miRNA silencing — a microRNA-RISC complex binds the 3'UTR in the cytoplasm and blocks ribosome loading, cutting translation without degrading the transcript.
Real-world relevance: mis-splicing and disrupted ncRNA regulation underlie diseases from spinal muscular atrophy (SMN2 exon skipping) to cancers driven by miRNA dysregulation.