The RNA-binding protein La is found in most eukaryotes, and despite being essential in many organisms, its function is not completely clear. Trypanosoma brucei, the causative agent of human African trypanosomiasis, encodes a 'classical' La protein (TbLa) composed of a La-motif, two RNA recognition motifs (RRM1 and RRM2α), a C-terminal short basic motif (SBM), and a nuclear localization signal (NLS). In T. brucei, like in most eukaryotes, position 34 of tRNATyr, -Asp, -Asn and -His is modified with queuosine (Q34). The steady-state levels of queuosine-modified tRNA in the insect form (procyclic) of T. brucei can fluctuate dynamically depending on growth conditions, but the mechanism(s) controlling Q34 levels are not well understood. A well-established function of La is in precursor-tRNA 3'-end metabolism, but in this work, we demonstrate that La also controls Q34-tRNA levels. Individual domain deletions showed that while deletion of La motif or RRM1 causes dysregulation of Q34-tRNA levels, no other domain plays a similar role. We also show that La is important for the normal balance of several additional tRNA modifications. These findings are discussed in the context of substrate competition between La and modification enzymes, also highlighting subcellular localization as a key determinant of tRNA function.

• MeSH
• Nucleoside Q metabolism   analogs & derivatives   MeSH
• RNA Processing, Post-Transcriptional * MeSH
• Protein Domains MeSH
• RNA-Binding Proteins * metabolism   chemistry   genetics   MeSH
• Protozoan Proteins * metabolism   chemistry   genetics   MeSH
• RNA, Transfer * metabolism   genetics   MeSH
• Trypanosoma brucei brucei * genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Nucleoside Q MeSH
• RNA-Binding Proteins * MeSH
• Protozoan Proteins * MeSH
• RNA, Transfer * MeSH