Intein is an intervening polypeptide which can catalytic self-cleavage from a pre-protein accompanied by the concomitant joining of the two flanking polypeptides (the extein) through a peptide bond.

白质内含是一个白质前体中的多序列，可以催化自白质前体中断裂，两侧的白质外接成成熟的白质。