Definition
Group II introns are a large class of self-catalytic ribozymes and mobile genetic elements found within the genes of all three domains of life. Ribozyme activity can usually occur under high-salt conditions in vitro for most group II introns. Certain highly reactive group II introns can undergo self-splicing under mild, near-physiologically relevant salt conditions. However, assistance from proteins is required for in vivo splicing. In contrast to group I introns, intron excision occurs in the absence of GTP and involves the formation of a lariat, with an A-residue branchpoint strongly resembling that found in lariats formed during splicing of nuclear pre-mRNA. It is hypothesized that pre-mRNA splicing may have evolved from group II introns, due to the similar catalytic mechanism as well as the structural similarity of the Group II Domain V substructure to the U6/U2 extended snRNA. Finally, their ability to site-specifically insert into DNA sites has been exploited as a tool for biotechnology. For example, group II introns can be modified to make site-specific genome insertions and deliver cargo DNA such as reporter genes or lox sites
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