A widespread self-cleaving ribozyme class is revealed by bioinformatics

To date, five classes of naturally occurring self-cleaving ribozymes have been reported. The bioinformatic discovery in bacteria and eukaryotes of twister RNAs, a new ribozyme class that contains a double pseudoknot fold, adds to the list of catalytic RNAs that have roles in cells. Ribozymes are noncoding RNAs that promote chemical transformations with rate enhancements approaching those of protein enzymes. Although ribozymes are likely to have been abundant during the RNA world era, only ten classes are known to exist among contemporary organisms. We report the discovery and analysis of an additional self-cleaving ribozyme class, called twister, which is present in many species of bacteria and eukarya. Nearly 2,700 twister ribozymes were identified that conform to a secondary structure consensus that is small yet complex, with three stems conjoined by internal and terminal loops. Two pseudoknots provide tertiary structure contacts that are critical for catalytic activity. The twister ribozyme motif provides another example of a natural RNA catalyst and calls attention to the potentially varied biological roles of this and other classes of widely distributed self-cleaving RNAs.