A Nuclear Encoded and Mitochondrial Imported Dicistronic tRNA Precursor in Trypanosoma brucei

LeBlanc, Allen J.; Yermovsky-Kammerer, Audra E.; Hajduk, Stephen L.

doi:10.1074/jbc.274.30.21071

Cited by 27 publications

(37 citation statements)

References 29 publications

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“…Polycistronic tRNA gene units are not the rule in eukaryotic systems and in yeast, animals, and plants, each tRNA gene is usually independently transcribed. Such unusual genomic organization has been reported only in a few cases, in particular in the protozoan Trypanosoma brucei where dicistronic tRNA precursors are found (LeBlanc et al 1999;Mottram et al 1991a,b). The presence of a short poly(T) motif at the 39 end of monocistronic and polycistronic tRNA gene units strongly suggests that most of the predicted tRNA genes are expressed in Chlamydomonas.…”

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confidence: 99%

On the Evolution and Expression of Chlamydomonas reinhardtii Nucleus-Encoded Transfer RNA Genes

et al. 2008

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In Chlamydomonas reinhardtii, 259 tRNA genes were identified and classified into 49 tRNA isoaccepting families. By constructing phylogenetic trees, we determined the evolutionary history for each tRNA gene family. The majority of the tRNA sequences are more closely related to their plant counterparts than to animals ones. Northern experiments also permitted us to show that at least one member of each tRNA isoacceptor family is transcribed and correctly processed in vivo. A short stretch of T residues known to be a signal for termination of polymerase III transcription was found downstream of most tRNA genes. It allowed us to propose that the vast majority of the tRNA genes are expressed and to confirm that numerous tRNA genes separated by short spacers are indeed cotranscribed. Interestingly, in silico analyses and hybridization experiments show that the cellular tRNA abundance is correlated with the number of tRNA genes and is adjusted to the codon usage to optimize translation efficiency. Finally, we studied the origin of SINEs, short interspersed elements related to tRNAs, whose presence in Chlamydomonas is exceptional. Phylogenetic analysis strongly suggests that tRNA Asp -related SINEs originate from a prokaryotic-type tRNA either horizontally transferred from a bacterium or originally present in mitochondria or chloroplasts.

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On the Evolution and Expression of Chlamydomonas reinhardtii Nucleus-Encoded Transfer RNA Genes

et al. 2008

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“…Although the role of 5Ј flanking sequences in localization of tRNAs to the mitochondria of trypanosomes is highly debated, previous studies have shown the presence of tRNA precursors in the mitochondria of T. brucei (15). Transcription of one precursor tRNA was shown to initiate 14 nucleotides upstream of the tRNA Ser coding sequence and extend through a 59-nucleotide intergenic sequence and a downstream tRNA Leu (15).…”

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“…Transcription of one precursor tRNA was shown to initiate 14 nucleotides upstream of the tRNA Ser coding sequence and extend through a 59-nucleotide intergenic sequence and a downstream tRNA Leu (15). These findings suggest that at least some tRNAs may be imported as precursors rather than as processed, mature tRNAs (15). Consistent with this result is the presence of RNase P activity in T. brucei mitochondria, although the ability of this activity to process in vitro imported precursor tRNAs to a mature size has not been demonstrated (9,23).…”

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“…The following protocol was adapted from that of LeBlanc et al (15). A 27-nt RNA oligonucleotide (5Ј-CG UACCGCGAUUAUG CUGAGUGAUAUC-3Ј) (Dharmacon) (500 pmol) was ligated to 10 g of mitochondrial and cytosolic RNA from pSer-Leu* and pSer-Leu* 1 transfectants.…”

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A Sequence Motif within Trypanosome Precursor tRNAs Influences Abundance and Mitochondrial Localization

Sherrer

Yermovsky-Kammerer

Hajduk

2003

Molecular and Cellular Biology

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Trypanosoma brucei lacks mitochondrial genes encoding tRNAs and must import nuclearly encoded tRNAs from the cytosol. The mechanism and specificity of this process remain unclear. We have identified a unique sequence motif, YGG(C/A)RRC, upstream of the genes encoding mitochondrially localized tRNAs in T. brucei. Both in vitro import studies and in vivo transfection studies indicate that deletion of the YGG(C/A)RRC sequence alters mitochondrial localization of tRNA Leu , and in vivo studies also show a decrease in the cellular abundance of tRNA Leu . These studies provide direct evidence for cis-acting RNA motifs within precursor tRNAs that facilitate the selection of tRNAs for mitochondrial import in trypanosomes. Furthermore, we found that mutations to the YGG(C/A)RRC sequence also altered the intracellular distribution of other endogenous tRNAs, suggesting a general role for this sequence in tRNA trafficking in trypanosomes.

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Transfer RNA travels from the cytoplasm to organelles

Rubio

Hopper

2011

WIREs RNA

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Transfer RNAs (tRNAs) encoded by the nuclear genome are surprisingly dynamic. Although tRNAs function in protein synthesis occurring on cytoplasmic ribosomes, tRNAs can transit from the cytoplasm to the nucleus and then again return to the cytoplasm by a process known as the tRNA retrograde process. Subsets of the cytoplasmic tRNAs are also imported into mitochondria and function in mitochondrial protein synthesis. The numbers of tRNA species that are imported into mitchondria differ among organisms, ranging from just a few to the entire set needed to decode mitochondrially encoded mRNAs. For some tRNAs, import is dependent on the mitochondrial protein import machinery, whereas the majority of tRNA mitochondrial import is independent of this machinery. Although cytoplasmic proteins and proteins located on the mitochondrial surface participating in the tRNA import process have been described for several organisms, the identity of these proteins differ among organisms. Likewise, the tRNA determinants required for mitochondrial import differ among tRNA species and organisms. Here, we present an overview and discuss the current state of knowledge regarding the mechanisms involved in the tRNA retrograde process and continue with an overview of tRNA import into mitochondria. Finally, we highlight areas of future research to understand the function and regulation of movement of tRNAs between the cytoplasm and organelles.

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A Nuclear Encoded and Mitochondrial Imported Dicistronic tRNA Precursor in Trypanosoma brucei

Cited by 27 publications

References 29 publications

On the Evolution and Expression of Chlamydomonas reinhardtii Nucleus-Encoded Transfer RNA Genes

On the Evolution and Expression of Chlamydomonas reinhardtii Nucleus-Encoded Transfer RNA Genes

A Sequence Motif within Trypanosome Precursor tRNAs Influences Abundance and Mitochondrial Localization

Transfer RNA travels from the cytoplasm to organelles

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