Small Cajal body specific RNA 18

small Cajal body-specific RNA 18 (also known as U91 or U4-8) is a type of small nuclear RNA which localises to the cajal bodies and proposed to guide the modification of RNA polymerase II transcribed spliceosomal RNAs U1, U2, U4, U5 and U12.[1]

small Cajal body-specific RNA 18
Predicted secondary structure and sequence conservation of SCARNA18
Identifiers
Symbol	SCARNA18
Alt. Symbols	U91
Rfam	RF00283
Other data
RNA type	Gene; snRNA; snoRNA; scaRNA
Domain(s)	Eukaryota
GO	GO:0006396 GO:0015030 GO:0005730
SO	SO:0000275
PDB structures	PDBe

This snoRNA U91 appears to be belong to the C/D box class of snoRNAs.[2] It was identified by Darzacq[1] and is predicted to guide the 2'O-ribose methylation of U4 snRNA C8. This C/D domain was later found associated in tandem with another C/D box domain U12-22. Both the doublet (U12-22/U4-8) and singlet (U4-8) forms of this snRNA have been purified from Hela cells.[1] The doublet form U12-22/U4-8 has been shown to localise to the nucleoplasm and is proposed to reside in the Cajal bodies whereas the U4-8 single domain appears to accumulate in the nucleolus.[3] In humans the genomic location of U12-88/U4-8 is intergenic and the purified transcript has been shown to possess a methylated guanosine cap suggesting it is independently transcribed by RNA pol II.[3]