Integration of the Tetrahymena group I intron into bacterial rRNA by reverse splicing in vivo

Horizontal gene transfer is thought to contribute to the wide distribution of group I introns among organisms. Integration of an intron into foreign RNA or DNA by reverse self-splicing, followed by reverse transcription and recombination, could lead to its transposition. Reverse self-splicing of group I introns has been demonstrated in vitro, but not in vivo. Here we report RNA-dependent integration of the Tetrahymena intron into the 23S rRNA in Escherichia coli. Analysis of products by Northern blot and reverse transcription–PCR amplification revealed precise intron insertion into a site homologous to the natural splice junction. Products are sensitive to treatment with RNase but not DNase and depend on the splicing activity of the intron. Partial reaction with 11 novel sites in the 23S RNA that are complementary to the guide sequence of the intron illustrates lower specificity than intron homing. Reverse splicing of the Tetrahymena intron in bacteria demonstrates the possibility of RNA-catalyzed transposition of group I introns in foreign hosts.