Small nucleolar RNA R21

In molecular biology, Small nucleolar RNA R21 is a non-coding RNA molecule which functions in the modification of other small [nuclear RNA]s. This type of modifying RNA is usually located in the nucleolus of the eukaryotic cell which is a major site of snRNA biogenesis. It is known as a small nucleolar RNA and also often referred to as a guide RNA.
snoRNA R21 belongs to the C/D box class of snoRNAs which contain the conserved sequence motifs known as the C box and the D box. Most of the members of the box C/D family function in directing site-specific 2'-O-methylation of substrate RNAs. Plant snoRNA R21 was identified in a screen of Arabidopsis thaliana.