Pre-RNA splicing mechanism. Illustration of the mechanism by which genetic material is modified in a process called splicing. The example here is pre-ribonucleic acid (RNA, yellow) from a eukaryotic cell. The sequence runs from top to bottom. The segment of RNA to be removed is shown in red (top) and is called the intron. An enzyme complex called a spliceosome excises the intron and merges the two sections (exons) to form the mature messenger RNA (mRNA, bottom). The spliceosome consists of small nuclear ribonucleoprotein particle (snRNP) subunits (blue and purple). For this artwork with labels, see C023/8868.