GROUP-II INTRONS - ELABORATE RIBOZYMES

Group II introns are found in organelle genomes of plants, fungi and a lgae as well as in some bacteria. Some group II introns have been show n to self-splice in vitro and thus constitute examples of ribozymes. T heir splicing pathway is analogous to the splicing pathway of nuclear pre-mRNA introns. They thus constitute simple models to analyze RNA ca talysis of this type of splicing reactions. In this review article, I will summarize our current state of understanding of the ribozyme acti vity of group II introns and show that their large size correlates wit h their ability to perform complex tasks. After discussing the similar ities found between group II and nuclear pre-mRNA introns, I will brie fly evoke how the ribozyme activity of group II introns might be invol ved in their transposition at the DNA level.