Visualization of a group II intron in the 23S rRNA of a stable ribosome.

Thousands of introns have been localized to rRNA genes throughout the three domains of life. The consequences of the presence of either a spliced or an unspliced intron in a rRNA for ribosome assembly and packaging are largely unknown. To help address these questions, and to begin an intron imaging study, we selected a member of the self-splicing group II intron family, which is hypothesized to be the progenitor not only of spliceosomal introns but also of non-LTR retrotransposons.