Type of Intron	Location	Splicing Mechanism
Group I	genes of eubacteria, bacteriophages, and eukaryotes	Self-splicing
Group II	genes of eubacteria, archaea, and eukaryotic organelles	Self-splicing
Nuclear pre-mRNA	Protein–encoding genes in the nucleus of eukaryotes	Spliceosomal
tRNA	tRNA genes of eubacteria, archaea, and eukaryotes	Enzymatic
Note: There are also several types of minor introns, including group III introns, twintrons, and archaeal introns.