Next ribosomal DNA repeating Ribosomal DNA repeating unit unit Ribosomal DNA transcription unit 18S 5.8s rRNA rRNA gene gene 28S rRNA gene DNA NTS ETS ITS ITS ETS pre-rRNA NTS Nontranscribed spacer ETS External transcribed spacer ITS Internal transcribed spacer The eukaryotic ribosomal DNA repeating unit The eukaryotic ribosomal DNA repeating unit