evolution. For the article ”Active self-splicing group I introns in 23S rRNA genes of hyperthermophilic bacteria, derived from introns in eukaryotic organelles,” by Camilla L. Nesbø and W. Ford Doolittle, which appeared in issue 19, September 16, 2003, of Proc. Natl. Acad. Sci. USA (100, 10806-10811; first published August 28, 2003; 10.1073/pnas.1434268100), the authors note that, due to an earlier misalignment, the position of the intron should be L1917, not L1926, and the intron should be annotated Tsu.bL1917 in Fig. 1b. The annotation of the sequence has been corrected in the GenBank database (accession no. AJ556793). Tsu.bL1917 is very similar in structure to two other introns in position L1917 (Chlorosarcina brevispinosa, GenBank accession no. L49150; and Chaetosphaeridium globosum, GenBank accession no. AF494279). The ORF in Tsu.bL1917 (i-Tsu1917b) clusters with the ORFs in these introns, as shown in Fig. 5, further supporting a recent transfer from a eukaryote.