Self-assembly of a group I intron from inactive oligonucleotide fragments.

The Azoarcus group I ribozyme was broken into four fragments, 39-63 nucleotides long, that can self-assemble into covalently contiguous ribozymes via RNA-directed recombination events. The fragments have no activity individually yet can cooperate through base pairing and tertiary interactions to produce stable trans complexes at 48 degrees C. These complexes can then catalyze a sequence of energy-neutral recombination reactions utilizing other oligomers as substrates, assembling covalent versions of the ribozyme. Up to 17% of the original fragments are converted into approximately 200 nucleotide products in 8 hr. Assembly occurs primarily by only one of many possible pathways, and the reaction is driven in the correct and forward direction by the burial of key base-pairing regions in stems after recombination. Autocatalysis, and hence self-replication, is inferred by a reaction rate increase upon doping the reaction with full-length RNA.