Discovery of group I introns in the nuclear small subunit ribosomal RNA genes of Acanthamoeba

The discovery of group I introns In small subunit nuclear rONA (nsrDNA) is becoming more common as the effort to generate phylogenies based upon nsrDNA sequences grows. In this paper we describe the discovery of the first two group I Introns in the nsrDNA from the genus Acanthamoeba. The introns are in different locations In the genes, and have no significant primary sequence similarity to each other. They are Identified as group I Introns by the conserved P, Q, R and S sequences (1), and the ability to fit the sequences to a consensus secondary structure model for the group I introns (1,2). Both Introns are absent from the mature srRNA. A BLAST search (3) of nucleic acid sequences present in GenBank and EMBL revealed that the A. griffinl intron was most similar to the nsrDNA group I Intron of the green alga Dunallella parve. A similar search found that the A.lentlculata intron was not similar to any of the other reported group I introns.