The 5S and 5.8S Ribosomal RNA Sequences of Tetrahymena thermophila and T. pyriformis1

The nucleotide sequences of the 5S rRNAs of Tetrahymena thermophila and two strains of T. pyriformis have been determined to be identical. The 5.8S rRNA sequences have also been determined; these sequences correct several errors in an earlier report. The 5.8S rRNAs of the two species differ at a single position. The sequencing results indicate that the species are of recent common ancestry. Molecular evidence that has been interpreted in the past as suggestive of an ancient divergence has been reviewed and found to be consistent with a T. pyriformis complex radiation beginning approximately 30–40 million years ago.