Abstract
The coding region for the Pneumocystis carinii small subunit rRNA (16S-like rRNA) contains 390 extra base pairs in a region that is highly conserved in other eukaryotic rRNA genes. The sequence has all the elements characteristic of group I self-splicing introns and interrupts the phylogenetically conserved helix proximal to the 3' terminus of the 16S-like rRNA. In vitro transcripts containing the putative group I intron were capable of undergoing a "self-splicing" reaction which required the presence of guanine nucleotide.