rRNA Biogenesis in Trypanosomes

rRNA processing is a complex and essential process that starts in the nucleolus, continues in the nucleoplasm, and is completed in the cytoplasm. The process involves the concerted action of the small nucleolar RNAs that direct cleavage at distinct sites in the intergenic spaces and modify the rRNA by 2{\textasciiacutex}-O-methylation and pseudouridylation. The process also requires protein factors such as endonucleases, ATPases, GTPases, and helicases that mediate the precise cleavage of the pre-rRNA in the intergenic regions and ensure the correct assembly of the two ribosomal subunits. In this chapter, I describe unique properties of this process in trypanosomes. As opposed to most eukaryotes, the large subunit of the rRNA is cleaved into two large subunits and additional small rRNA fragments. The unique repertoire of small nucleolar RNAs (snoRNAs) is described, emphasizing the lack of conventional snoRNAs involved in rRNA processing and the presence of trypanosome-specific snoRNAs. Finally, the protein factors involved in this process are described, focusing on factors whose function was elucidated in trypanosomes, and on a bioinformatics survey to detect protein factors involved in this process in other eukaryotes.