Inteins are segments of protein which excise themselves from a precursor protein and mediate the rejoining of the remainder of the precursor (the extein). Most inteins consist of a splicing domain which is split into two segments by a homing endonuclease domain. This domain represents the splicing domain [1].

1: Crystal structure of a mini-intein reveals a conserved catalytic module involved in side chain cyclization of asparagine during protein splicing. Ding Y, Xu MQ, Ghosh I, Chen X, Ferrandon S, Lesage G, Rao Z; J Biol Chem. 2003;278:39133-39142. PMID:12878593