具有自我催化能力，将自身的某些部位切除的现象称为自我剪接。在酵母和真菌的线粒体mRNA和tRNA前体加工、叶绿体的tRNA 和rRNA前体加工、某些细菌病毒的mRNA前体加工中都发现了自我剪接现象。

自我剪接(self-splicing)

The basic reaction for this kind of splicing is different from the normal splicing: there is no attacking adenosine nucleotide, and no lariat is formed. Instead, the 5’ splice site is broken by attack from a G outside of the transcript. Then, the free end of the exon attacks the 3’ splice site, displacing the intron and forming a new bond with the next exon. Introns that are spliced this way are called a group I introns.

这种剪接的基本反应与正常的剪接反应不同：它没有进攻性的腺嘌呤核苷酸，也不形成套索结构。相反，内含子在5’剪接位点受到的威胁来自于转录产物之外的鸟嘌呤核苷酸。之后外显子的自由末端发起对3’剪接位点的攻击，替代了内含子而与后面的外显子形成新的键。以这样的方式进行剪接的内含子称为I类内含子。