Small nucleolar RNA
Prior to cleavage by exo- and endonucleases, the pre-rRNA undergoes a complex pattern of nucleoside modifications.
[2] In order to carry out modification, each snoRNA associates with at least four core proteins in an RNA/protein complex referred to as a small nucleolar ribonucleoprotein particle (snoRNP).
The HGNC, in collaboration with snoRNABase and experts in the field, has approved unique names for human genes that encode snoRNAs.
This recognition sequence is bipartite (constructed from the two different arms of the loop region) and forms complex pseudo-knots with the target RNA.
[13] The H/ACA snoRNP has been implicated in the rare genetic disease dyskeratosis congenita (DKC) due to its affiliation with human telomerase.
An unusual guide snoRNA U85 that functions in both 2′-O-ribose methylation and pseudouridylation of small nuclear RNA (snRNA) U5 has been identified.
[18] For example, it appears that the C/D box snoRNA SNORD115 regulates the alternative splicing of the serotonin 2C receptor mRNA via a conserved region of complementarity.
[19][20] Another C/D box snoRNA, SNORD116, that resides in the same cluster as SNORD115 has been predicted to have 23 possible targets within protein coding genes using a bioinformatic approach.
The modifications do not appear to be essential but are known to subtly enhance the RNA folding and interaction with ribosomal proteins.
[5] A novel method, Nm-REP-seq, was developed for enriching 2'-O-Methylations guided by C/D snoRNAs by using RNA exoribonuclease (Mycoplasma genitalium RNase R, MgR) and periodate oxidation reactivity to eliminate 2'-hydroxylated (2'-OH) nucleosides.
SnoRNAs are also shown to be located in intergenic regions, ORFs of protein coding genes, and UTRs.
It has been shown that human ACA45 is a bona fide snoRNA that can be processed into a 21-nucleotides-long mature miRNA by the RNAse III family endoribonuclease dicer.
[34] This snoRNA product has previously been identified as mmu-miR-1839 and was shown to be processed independently from the other miRNA-generating endoribonuclease drosha.
[19] In November 2012, Schubert et al. revealed that specific RNAs control chromatin compaction and accessibility in Drosophila cells.
[37] In July 2023, Lin et al. showed that snoRNAs have the potential to guide other RNA modifications, specifically N6-methyladenosine, however this is subject to further investigation.
[22] TB11Cs4H1 is a member of the H/ACA-like class of non-coding RNA (ncRNA) molecule (a snoRNA) that guide the sites of modification of uridines to pseudouridines of substrate RNAs.
