Group II intron splicing in vivo by first-step hydrolysis

Nature. 1998 Feb 26;391(6670):915-8. doi: 10.1038/36142.


Group I, group II and spliceosomal introns splice by two sequential transesterification reactions. For both spliceosomal and group II introns, the first-step reaction occurs by nucleophilic attack on the 5' splice junction by the 2' hydroxyl of an internal adenosine, forming a 2'-5' phosphodiester branch in the intron. The second reaction joins the two exons with a 3'-5' phosphodiester bond and releases intron lariat. In vitro, group II introns can self-splice by an efficient alternative pathway in which the first-step reaction occurs by hydrolysis. The resulting linear splicing intermediate participates in normal second-step reactions, forming spliced exon and linear intron RNAs. Here we show that the group II intron first-step hydrolysis reaction occurs in vivo in place of transesterification in the mitochondria of yeast strains containing branch-site mutations. As expected, the mutations block branching, but surprisingly still allow accurate splicing. This hydrolysis pathway may have been a step in the evolution of splicing mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Esterification
  • Genes, Fungal
  • Hydrolysis
  • Introns*
  • Mitochondria / metabolism
  • Mutagenesis, Site-Directed
  • RNA Splicing*
  • RNA, Fungal / metabolism
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism


  • RNA, Fungal