User:Htafer/SNORD22

snoRNA U22 (also known as SNORD22) is a non-coding RNA (ncRNA) molecule which functions in the modification of other small nuclear RNAs (snRNAs). 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 (snoRNA) and also often referred to as a guide RNA.

U22 belongs to the C/D box class of snoRNAs which contain the conserved sequence motifs known as the C box (UGAUGA) and the D box (CUGA). In contrast to most of the members of the box C/D family which function in directing site-specific 2'-O-methylation of substrate RNAs, SNORD22 belongs to the small group of snoRNAs that govern the cleavage of the ribosomal RNA precursors. In the absence of SNORD22, mature 18S rRNA fails to accumulate



SNORD22 is expressed from the conserved host gene SNHG1 (also known as UHG), which shows little sequence conservation on the exons and besides SNORD22 harbours several other snoRNAs . Expression of SNORD22 is known in human and mouse , Xenopus , and rhesus . In addition, annotates the platypus C/D box snoRNA Oa1907 as an ortholog of the human SNORD22 and Oa1925 as an ortholog of a human SNORD22 pseudogene. With a length between 116 nt (Petromyzon) and 129 nt (Microcebus), it just slightly exceeds the typical length range for box C/D snoRNAs.

The sequence of SNORD22 is well-conserved. Homologs are described throughout the gnathostomes in snoOPY (http://snoopy.med.miyazaki-u.ac.jp), and additional SNORD22 sequences are detectable in basal vertebrates and in the cephalochordate Branchiostoma floridae. The host gene SNHG1 also harbours several other unrelated, canonical snoRNAs namely snR56, SNORD25, SNORD26, SNORD27, SNORD28, SNORD29, SNORD30, SNORD31. Some of these snoRNAs, including SNORD22, are duplicated in some species. The genomic position of the host genes SNHG1 is syntenically conserved within tetrapods (between SLC3A2 and WDR74) and, at a different locus, within teleosts (between B3GAT3 and ARL2).