18S ribosomal RNA

18S ribosomal RNA is the eukaryotic nuclear homologue of 16S ribosomal RNA; this is the structural RNA for the small component of eukraryotic cytoplasmic ribosomes, and thus one of the basic components of all eukayotic cells.

It has been used to support the grouping of birds with mammals, but this has recently been disputed.

General References
Lodish, H. Molecular Cell Biology 3rd ed. Freeman, 1995.