18S ribosomal RNA (abbreviated
18S rRNA) is a part of the
ribosomal RNA. The S in 18S represents
Svedberg units. 18S rRNA is a component of the small
eukaryotic ribosomal subunit (
40S). 18S rRNA is the structural RNA for the small component of eukaryotic cytoplasmic
ribosomes, and thus one of the basic components of all eukaryotic cells.