Every type of nucleic acid in cells undergoes programmed chemical post-transcriptional modification. Generally, modification enzymes use substrates derived from intracellular metabolism, one exception is queuine (q)/queuosine (Q), which eukaryotes obtain from their environment; made by bacteria and ultimately taken into eukaryotic cells via currently unknown transport systems. Here, we use a combination of molecular, cell biology and biophysical approaches to show that in Trypanosoma brucei tRNA Q levels change dynamically in response to concentration variations of a sub-set of amino acids in the growth media. Most significant were variations in tyrosine, which at low levels lead to increased Q content for all the natural tRNAs substrates of tRNA-guanine transglycosylase (TGT). Such increase results from longer nuclear dwell time aided by retrograde transport following cytoplasmic splicing. In turn high tyrosine levels lead to rapid decrease in Q content. Importantly, the dynamic changes in Q content of tRNAs have negligible effects on global translation or growth rate but, at least, in the case of tRNATyr it affected codon choice. These observations have implications for the occurrence of other tunable modifications important for 'normal' growth, while connecting the intracellular localization of modification enzymes, metabolites and tRNAs to codon selection and implicitly translational output.

• MeSH
• aminokyseliny metabolismus   MeSH
• chromatografie kapalinová metody   MeSH
• guanin analogy a deriváty   metabolismus   MeSH
• kodon genetika   metabolismus   MeSH
• nukleosid Q metabolismus   MeSH
• pentosyltransferasy genetika   metabolismus   MeSH
• protozoální proteiny genetika   metabolismus   MeSH
• RNA transferová Tyr genetika   metabolismus   MeSH
• RNA transferová genetika   metabolismus   MeSH
• sestřih RNA MeSH
• tandemová hmotnostní spektrometrie metody   MeSH
• Trypanosoma brucei brucei genetika   metabolismus   MeSH
• tyrosin metabolismus   MeSH
• živiny metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• aminokyseliny MeSH
• guanin MeSH
• kodon MeSH
• nukleosid Q MeSH
• pentosyltransferasy MeSH
• protozoální proteiny MeSH
• queuine tRNA-ribosyltransferase MeSH Prohlížeč
• queuine MeSH Prohlížeč
• RNA transferová Tyr MeSH
• RNA transferová MeSH
• tyrosin MeSH

Transfer RNAs play a key role in protein synthesis. Following transcription, tRNAs are extensively processed prior to their departure from the nucleus to become fully functional during translation. This includes removal of 5′ leaders and 3′ trailers by a specific endo- and/or exonuclease, 3′ CCA tail addition, posttranscriptional modifications and in some cases intron removal. In this minireview, the critical factors of nuclear tRNA trafficking are described based on studies in classical models such as yeast and human cell lines. In addition, recent findings and identification of novel regulatory loops of nuclear tRNA trafficking in trypanosomes are discussed with emphasis on tRNA modifications. The comparison between the representatives of opisthokonts and excavates serves here to understand the evolutionary conservation and diversity of nuclear tRNA export mechanisms.

• Klíčová slova
• Nuclear tRNA export, Trypanosoma brucei, tRNA modification,
• MeSH
• buněčné linie MeSH
• lidé MeSH
• RNA jaderná genetika   metabolismus   MeSH
• RNA transferová genetika   metabolismus   MeSH
• Saccharomyces cerevisiae genetika   metabolismus   MeSH
• Trypanosoma genetika   metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• RNA jaderná MeSH
• RNA transferová MeSH

Kinetoplastids, including Trypanosoma brucei, control gene expression primarily at the posttranscriptional level. Nuclear mRNA export is an important, but understudied, step in this process. The general heterodimeric export factors, Mex67/Mtr2, function in the export of mRNAs and tRNAs in T. brucei, but RNA binding proteins (RBPs) that regulate export processes by controlling the dynamics of Mex67/Mtr2 ribonucleoprotein formation or transport have not been identified. Here, we report that DRBD18, an essential and abundant T. brucei RBP, associates with Mex67/Mtr2 in vivo, likely through its direct interaction with Mtr2. DRBD18 downregulation results in partial accumulation of poly(A)+ mRNA in the nucleus, but has no effect on the localization of intron-containing or mature tRNAs. Comprehensive analysis of transcriptomes from whole-cell and cytosol in DRBD18 knockdown parasites demonstrates that depletion of DRBD18 leads to impairment of nuclear export of a subset of mRNAs. CLIP experiments reveal the association of DRBD18 with several of these mRNAs. Moreover, DRBD18 knockdown leads to a partial accumulation of the Mex67/Mtr2 export receptors in the nucleus. Taken together, the current study supports a model in which DRBD18 regulates the selective nuclear export of mRNAs by promoting the mobilization of export competent mRNPs to the cytosol through the nuclear pore complex.

• Klíčová slova
• FISH, RNA binding protein, RNAseq, mRNA export, nucleoporin, trypanosome,
• MeSH
• aktivní transport - buněčné jádro MeSH
• genový knockdown metody   MeSH
• membránové transportní proteiny metabolismus   MeSH
• messenger RNA metabolismus   MeSH
• nukleocytoplazmatické transportní proteiny metabolismus   MeSH
• proteiny vázající RNA genetika   metabolismus   MeSH
• protozoální proteiny genetika   metabolismus   MeSH
• regulace genové exprese MeSH
• RNA transferová metabolismus   MeSH
• transkriptom MeSH
• transport RNA MeSH
• Trypanosoma brucei brucei genetika   metabolismus   MeSH
• vazba proteinů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• membránové transportní proteiny MeSH
• messenger RNA MeSH
• nukleocytoplazmatické transportní proteiny MeSH
• proteiny vázající RNA MeSH
• protozoální proteiny MeSH
• RNA transferová MeSH

Transfer RNAs (tRNAs) are key players in protein synthesis. To be fully active, tRNAs undergo extensive post-transcriptional modifications, including queuosine (Q), a hypermodified 7-deaza-guanosine present in the anticodon of several tRNAs in bacteria and eukarya. Here, molecular and biochemical approaches revealed that in the protozoan parasite Trypanosoma brucei, Q-containing tRNAs have a preference for the U-ending codons for asparagine, aspartate, tyrosine and histidine, analogous to what has been described in other systems. However, since a lack of tRNA genes in T. brucei mitochondria makes it essential to import a complete set from the cytoplasm, we surprisingly found that Q-modified tRNAs are preferentially imported over their unmodified counterparts. In turn, their absence from mitochondria has a pronounced effect on organellar translation and affects function. Although Q modification in T. brucei is globally important for codon selection, it is more so for mitochondrial protein synthesis. These results provide a unique example of the combined regulatory effect of codon usage and wobble modifications on protein synthesis; all driven by tRNA intracellular transport dynamics.

• MeSH
• antikodon genetika   MeSH
• buněčné jádro genetika   ultrastruktura   MeSH
• cytoplazma genetika   ultrastruktura   MeSH
• guanosin genetika   MeSH
• kodon genetika   MeSH
• konformace nukleové kyseliny * MeSH
• mitochondrie genetika   MeSH
• nukleosid Q genetika   MeSH
• posttranskripční úpravy RNA genetika   MeSH
• proteosyntéza genetika   MeSH
• RNA transferová genetika   ultrastruktura   MeSH
• Trypanosoma brucei brucei genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• antikodon MeSH
• guanosin MeSH
• kodon MeSH
• nukleosid Q MeSH
• RNA transferová MeSH

Transfer RNAs (tRNAs) are central players in protein synthesis, which in Eukarya need to be delivered from the nucleus to the cytoplasm by specific transport receptors, most of which belong to the evolutionarily conserved beta-importin family. Based on the available literature, we identified two candidates, Xpo-t and Xpo-5 for tRNA export in Trypanosoma brucei. However, down-regulation of expression of these genes did not disrupt the export of tRNAs to the cytoplasm. In search of alternative pathways, we tested the mRNA export complex Mex67-Mtr2, for a role in tRNA nuclear export, as described previously in yeast. Down-regulation of either exporter affected the subcellular distribution of tRNAs. However, contrary to yeast, TbMex67 and TbMtr2 accumulated different subsets of tRNAs in the nucleus. While TbMtr2 perturbed the export of all the tRNAs tested, silencing of TbMex67, led to the nuclear accumulation of tRNAs that are typically modified with queuosine. In turn, inhibition of tRNA nuclear export also affected the levels of queuosine modification in tRNAs. Taken together, the results presented demonstrate the dynamic nature of tRNA trafficking in T. brucei and its potential impact not only on the availability of tRNAs for protein synthesis but also on their modification status.

• MeSH
• beta karyoferiny antagonisté a inhibitory   genetika   metabolismus   MeSH
• biologický transport MeSH
• buněčné jádro genetika   metabolismus   MeSH
• cytoplazma genetika   metabolismus   MeSH
• konformace nukleové kyseliny MeSH
• malá interferující RNA genetika   metabolismus   MeSH
• messenger RNA genetika   metabolismus   MeSH
• nukleocytoplazmatické transportní proteiny antagonisté a inhibitory   genetika   metabolismus   MeSH
• nukleosid Q chemie   metabolismus   MeSH
• proteosyntéza MeSH
• protozoální proteiny antagonisté a inhibitory   genetika   metabolismus   MeSH
• regulace genové exprese MeSH
• RNA protozoální chemie   genetika   metabolismus   MeSH
• RNA transferová chemie   genetika   metabolismus   MeSH
• signální transdukce MeSH
• Trypanosoma brucei brucei genetika   metabolismus   MeSH
• vazba proteinů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• beta karyoferiny MeSH
• malá interferující RNA MeSH
• messenger RNA MeSH
• nukleocytoplazmatické transportní proteiny MeSH
• nukleosid Q MeSH
• protozoální proteiny MeSH
• RNA protozoální MeSH
• RNA transferová MeSH