Elucidating the Role of C/D snoRNA in rRNA Processing and Modification inTrypanosoma brucei

Abstract

Most eukaryotic C/D small nucleolar RNAs (snoRNAs) guide 2-O methylation (Nm) on rRNA and are also involved in rRNA processing. The four core proteins that bind C/D snoRNA in Trypanosoma brucei are fibrillarin (NOP1), NOP56, NOP58, and SNU13. Silencing of NOP1 by RNA interference identified rRNAprocessing and modification defects that caused lethality. Systematic mapping of 2-O-methyls on rRNA revealed the existence of hypermethylation at certain positions of the rRNA in the bloodstream form of the parasites, suggesting that this modification may assist the parasites in coping with the major temperature changes during cycling between their insect and mammalian hosts. The rRNA-processing defects of NOP1-depleted cells suggest the involvement of C/D snoRNA in trypanosome-specific rRNA-processing events to generate the small rRNA fragments. MRP RNA, which is involved in rRNA processing, was identified in this study in one of the snoRNA gene clusters, suggesting that trypanosomes utilize a combination of unique C/D snoRNAs and conserved snoRNAs for rRNA processing.

Cl gene cluster encoding several small nucleolar RNAs: a comparison amongst trypanosomatids

“…However, snoRNAs Cl2 and Cl3 exhibited greater target methylation as compared to Cl1 (Barth et al 2008). These results showed that other factors aside from copy number and expression level were influencing the modification guiding process, such as the presence of secondary structure at the modification site.…”

“…It has been reported recently that position U611 within the LSU is 66.2% hypermethylated in bloodstream versus procyclic forms; this may help the parasite to adapt to a higher vertebrate host temperature (Barth et al 2008).…”

“…snoRNAs (a type of ncRNA) are involved in RNA modifications leading to correct RNA folding and RNA-RNA and RNA-protein interactions (Zemann et al 2006). It is known that snoRNAs from trypanosomatids are involved not only in rRNA processing and modifications but also in snRNA modifications thereby affecting protein synthesis and trans-splicing (Barth et al , 2008. In this study, the Cl gene cluster encoding several snoRNAs was characterised in T. rangeli and compared to those from T. cruzi, T.…”

“…This range is in accordance with the minimum 10 nt distance needed for the proper processing of each snoRNA (Xu et al 2001). Indeed, Cl gene cluster C/D box snoRNA expression has been described in L. collosoma (Xu et al 2001) and T. brucei (Barth et al 2008). Although there is no specific expression data from Cl-H/ACA snoRNAs, other B2 cluster H/ACA snoRNAs have been detected in L. collosoma by Northern blot or primer extension analysis (Xu et al 2001 suggesting the expression of these snoRNAs as well.…”

Families of H/ACA ncRNA molecules in Trypanosomatids

“…These ribosomal modifications are crucial for protein synthesis and fidelity and govern the sensitivity to ribosome-based antibiotics. [2][3][4][5][6][7] In most eukaryotes, the pseudouridylation guide snoRNAs consist of two hairpins, a 5' hairpin followed by a single-stranded H-box (ANANNA, where N stands for any nucleotide) and a 3' hairpin followed by an ACA-box. The snoRNA's pseudouridylation pocket consists of two short sequences that are complementary to the flanking rRNA sequence of the uridine to be converted.…”