RNA splicing

RNA splicing is film editing for genes. The first RNA copy of a eukaryotic gene contains both the parts that carry the message and stretches of filler in between. Splicing snips out the filler and stitches the meaningful pieces together into a clean, continuous message ready to be read.

The filler segments are called introns and the kept segments are exons. A large molecular machine, the spliceosome — built from proteins and small RNAs — recognises the boundaries of each intron, cuts the RNA precisely there, and joins the flanking exons. Accuracy matters down to the single base, because a one-base slip would shift the reading frame and garble the protein.

Splicing is more than tidying up. By choosing which exons to keep, a cell can build several different messages, and thus several proteins, from one gene. That makes splicing both a step in producing mRNA and a powerful point of gene regulation, especially in animals where most genes are interrupted by introns.