The small-subunit ribosomal RNA gene sequences from the hypotrichous ciliates Oxytricha nova and Stylonychia pustulata

We have determined the complete nucleotide sequence of the small- subunitribosomal RNA genes for the ciliate protozoans Stylonychia pustulata andOxytricha nova. The sequences are homologous and sufficiently similar thatthese organisms must be closely related. In a phylogeny inferred fromcomparisons of several eukaryotic small-subunit ribosomal RNAs, thedivergence of the ciliates from the eukaryotic line of descent is seen tocoincide with the radiation of the plants, the animals, and the fungi. Thisradiation is preceded by the divergence of the slime mold, Dictyosteliumdiscoideum.