Fixation and accumulation of thermotolerant catalytic competence of a pair of ligase ribozymes through complex formation and cross ligation.

In the early stages of the hypothetical RNA world, some primitive RNA catalysts (ribozymes) may have emerged through self-assembly of short RNA oligomers. Although they may be unstable against temperature fluctuations and other environmental changes, ligase ribozymes (ribozymes with RNA strand-joining activity) may resolve structural instability of self-assembling RNAs by converting them to the corresponding unimolecular formats. To investigate this possibility, we constructed a model system using a cross-ligation system composed of a pair of self-assembling ligase ribozymes. Their abilities to act as catalysts, substrates, and a cross-ligation system were analyzed with or without thermal pretreatment before the reactions. A pair of self-assembling ligase ribozymes, each of which can form multiple conformations, demonstrated that thermotolerance was acquired and accumulated through complex-formation that stabilized the active forms of the bimolecular ribozymes and also cross-ligation that produced the unimolecular ribozymes.

The transDSL ligase ribozyme can utilize various forms of modules to clamp its substrate and enzyme units.

TransDSL is an RNA ligase ribozyme whose enzyme unit joins two RNA fragments constituting a substrate. The enzyme unit recognizes the substrate by means of two clamp modules. We constructed active variants by replacing the original clamp module with various types of interactions. Such flexible modularity would be advantageous in the application of this ribozyme in nanobiotechnology.