text: Splicing occurs in all the kingdoms or domains of life, however, the extent and types of splicing can be very different between the major divisions.  Eukaryotes splice many protein-coding messenger RNAs and some non-coding RNAs. Prokaryotes, on the other hand, splice rarely and mostly non-coding RNAs. Another important difference between these two groups of organisms is that prokaryotes completely lack the spliceosomal pathway.
  Because spliceosomal introns are not conserved in all species, there is debate concerning when spliceosomal splicing evolved.  Two models have been proposed: the intron late and intron early models (see intron evolution).