- U17XS8, a small nucleolar RNA with a 12 nt complementarity to 18S rRNA and coded by a sequence repeated in the six introns of Xenopus laevis ribosomal protein S8 gene. Cecconi, F., Mariottini, P., Loreni, F., Pierandrei-Amaldi, P., Campioni, N., Amaldi, F. Nucleic Acids Res. (1994)