Group II Introns

Abstract The self‐splicing group II introns are among the largest naturally occurring ribozymes and have been found primarily in organellar genomes of plants, fungi, bacteria, proteobacteria, and blue algae. More recently, a group II intron was found in a primitive metazoan. More than 200 different group II introns have been identified to date. All group II introns have a conserved secondary structure composed of six stem‐loop structures termed domains D1–D6, which are arranged around a central wheel and provide distinct contributions to intron function. Group II introns catalyze their own excision from pre‐RNA by two consecutive transesterifications and concomitant splicing of the flanking exons. The reaction requires Mg 2+ ions, which are directly involved in catalysis and are also needed for proper folding of the intron. Intriguingly, group II introns share several mechanistic and structural features with the eukaryotic spliceosome, which suggests an evolutionary relationship. In vivo , group II intron splicing is generally assisted by proteins. With the help of proteins, some group II introns can also reverse the splicing reaction and integrate themselves into target genomes; this process resembles transposition of non‐LTR retrotransposons and can be exploited for biotechnological applications.