Pseudouridines and ribosome heterogeneity: Towards specialized translation

Pseudouridine (Ψ) is one of the most prominent RNA modifications present on various non-coding RNAs such as tRNA, rRNA and snRNA. Ψ (a C5-glycoside isomer of uridine) is formed by breakage of the N1-glycosyl bond followed by 180° base rotation and formation of a C5-glycosyl bond. This modification is found on non-coding RNA such as rRNA, tRNA and snRNAs. Many of these modifications are guided by small nucleolar (snoRNAs). In our group, we study role of Ψs in the two life stages of the parasite Trypanosoma brucei and Leishmania species and its role in adaptation during cycling of the parasite between its two hosts the insect and the mammalian host. We recently demonstrated that Ψs level on both rRNA and snRNAs changes during cycling of the parasite, and many sites are hypermodified in the bloodstream form (BSF) that propagates in the mammalian host (Chikne et al., Sci. rep 2016). The number of Ψs on snRNA is the highest found so far in nature (Rajan et al., NAR 2019). To study the functional significance of the hypermodification we used CRISPR-Cas9 to knock-out the pseudouridine synthase bound to the snoRNAs (CBF5) and certain snoRNAs guiding these modifications. sKO of snoRNAs or sKO of CBF5 affected growth and generated specific defects in translation. These defects emerge specifically because of reduction in the level of the Ψ. Leishmania sKO for snoRNAs are affected virulent. We are currently examining the intriguing possibility that Ψ modification affects stage specific translation in these parasites.