In molecular biology, non-coding RNAs (ncRNA) are RNA molecules that have a function but are not translated into proteins. Small nucleolar RNAs (snoRNAs), one of the largest classes of ncRNA, are further subdivided into the two major C/D and H/ACA snoRNA families. snoRNA serve as guide RNAs for 2'-O-methylation and pseudouridylation of specific nucleotides and indicate the site of modification by direct base pairing with the target RNA. The majority of these snoRNAs are responsible for the post-transcriptional modification of ribosomal RNAs (rRNA) and in some cases of small nuclear RNAs (sRNAs). These post-transcriptional modifications are crucial for rRNA processing, stability and maturation.

The H/ACA snoRNAs that guide pseudouridylation in Trypanosomes consist of a single-hairpin followed by an AGA-box. These H/ACA snoRNA contain a pseudouridylation pocket that guides the H/ACA snoRNA to the correct region of its target rRNA. The pseudouridylation pocket ensures modification of the correct uridine, as it contains two short sequences that are complementary to the target RNA. In addition it is able to basepair with the regions flanking the uridine in need of modification. Trypanosomal snoRNAs differ in both sequence and structure to eukaryotic snoRNAs as they contain one stem loop and an AGA-box at the 3' end. Despite these differences, trypanosomal snoRNAs function identically to eukaryotic snoRNAs and since the discovery of single stem H/ACA snoRNAs in Trypanosomes, similar single hairpin ncRNAs have been discovered in Archea and Euglena. The table below summarizes the H/ACA snoRNAs and the corresponding target sites identified in Trypanosomes.

H/ACA snoRNAs identified in Trypanosomes

H/ACA ID Target Reference TB3Cs2H1 ?308-L5 Myslyuk et al. 2008 TB3Cs2H2 ?1658-L5 Myslyuk et al. 2008 TB8Cs4H1 ?358-L3 Myslyuk et al. 2008 TB8Cs4H2 ?141-L3 Myslyuk et al. 2008 TB9Cs6H1 ?199-L5, ?29-5.8S Myslyuk et al. 2008 TB9Cs6H2 ?1653-L5 Myslyuk et al. 2008 TB10Cs5H1 ?1254-L3 Myslyuk et al. 2008 TB10Cs5H2 ?131-S Myslyuk et al. 2008 TB10Cs5H3 ?1276-S Myslyuk et al. 2008 TB11Cs5H1 ?1710-S Myslyuk et al. 2008 TB11Cs5H2 ?176-L3 Myslyuk et al. 2008 TB11Cs5H3 ?1314-L3 Myslyuk et al. 2008 TB6Cs1H1 ?380-L3 Liang et al. 2005 TB6Cs1H2 Liang et al. 2005 TB6Cs1H3 ?662-S Liang et al. 2005 TB6Cs1H4 ?824-L5 Liang et al. 2005 TB6Cs2H1 ?1001-SSU Liang et al. 2005 TB8Cs2H1 ?1113-S Liang et al. 2005 TB8Cs3H1 ?1423-S Liang et al. 2005 TB9Cs1H1 ?1088-S,?1272-L3 Liang et al. 2005 TB9Cs1H2 ?1619-S Liang et al. 2005 TB9Cs1H3 ?1250-L5 Liang et al. 2005 TB9Cs2H1 ?617-L3 Liang et al. 2005 TB9Cs2H2 ?1412-L5 Liang et al. 2005 TB9Cs3H1 ?1208-L3 Liang et al. 2005 TB9Cs3H2 ?1103-L5 Liang et al. 2005 TB9Cs4H1 ?2123-S Liang et al. 2005 TB9Cs4H2 ?1336-L3 Liang et al. 2005 TB9Cs4H3 Liang et al. 2005 TB10Cs1H1 ?659-L3 Liang et al. 2005 TB10Cs1H2 ?901-L5 Liang et al. 2005 TB10Cs1H3 ?40-S Liang et al. 2005 TB10Cs2H1 ?1167-L3 Liang et al. 2005 TB10Cs2H2 ?1173-L5 Liang et al. 2005 TB10Cs3H1 ?263-S Liang et al. 2005 TB10Cs3H2 ?397-L3 Liang et al. 2005 TB10Cs4H1 ?2248-L5 Liang et al. 2005 TB10Cs4H2 ?1186-S Liang et al. 2005 TB10Cs4H3 ?1773-L5 Liang et al. 2005 TB10Cs4H4 ?505-S Liang et al. 2005 TB11Cs2H1 ?28 SL Liang et al. 2005 TB11Cs3H1 ?1308-L3 Liang et al. 2005 TB11Cs3H2 ?475-L3 Liang et al. 2005 TB11Cs4H1 ?1357-L3 Liang et al. 2005 TB11Cs4H2 ?566-L3 Liang et al. 2005 TB11Cs4H3 ?61-S Liang et al. 2005

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