Pathway: tRNA modification in the mitochondrion
Reactions in pathway: tRNA modification in the mitochondrion :
tRNA modification in the mitochondrion
The 22 tRNAs encoded by the mitochondrial genome are modified in the mitochondrial matrix by enzymes encoded in the nucleus and imported into mitochondria (reviewed in Suzuki et al. 2011, Salinas-Giege et al. 2015). Some enzymes such as PUS1 and TRIT1 are located in more than one compartment and modify both mitochondrial tRNAs and cytosolic tRNAs. Other enzymes such as MTO1, TRMU, and TRMT61B are exclusively mitochondrial.
Modifications near the anticodon and near the 3' end of tRNAs tend to affect interaction of the tRNA with mRNA within ribosomes and with tRNA synthetases, respectively. Modifications in other regions, typically in the "core" of the tRNA tend to affect folding and stability of the tRNA (reviewed in Hou et al. 2015). The unusual modification 5-taurinomethyl-2-thiouridine-34 in the anticodon of at least 3 tRNAs is found only in mammalian mitochondria and mutations that affect the responsible biosynthetic enzymes (GTPBP3, MTO1, TRMU) cause mitochondrial dysfunction and disease (reviewed in Torres et al. 2014).
Modifications near the anticodon and near the 3' end of tRNAs tend to affect interaction of the tRNA with mRNA within ribosomes and with tRNA synthetases, respectively. Modifications in other regions, typically in the "core" of the tRNA tend to affect folding and stability of the tRNA (reviewed in Hou et al. 2015). The unusual modification 5-taurinomethyl-2-thiouridine-34 in the anticodon of at least 3 tRNAs is found only in mammalian mitochondria and mutations that affect the responsible biosynthetic enzymes (GTPBP3, MTO1, TRMU) cause mitochondrial dysfunction and disease (reviewed in Torres et al. 2014).
Genes encoding transfer RNAs (tRNAs) are transcribed by RNA polymerase III in the nucleus and by mitochondrial RNA polymerase in the mitochondrion.
In the nucleus transcription reactions produce precursor tRNAs (pre-tRNAs) that have extra 5' leaders, 3' trailers, and, in some cases, introns which are removed by enzymes and enzyme complexes: RNase P cleaves the 5' leader, RNase Z cleaves the 3' trailer, TRNT1 polymerizes CCA onto the resulting 3' end, the TSEN complex cleaves at each end of the intron, and the tRNA ligase complex ligates the resulting exons (reviewed in Rossmanith et al. 1995, Phizicky and Hopper 2010, Suzuki et al. 2011, Abbott et al. 2014, Li and Mason 2014). The nucleotides within tRNAs undergo further chemical modifications such as methylation and deamination by a diverse set of enzymes (reviewed in Helm and Alfonzo 2014, Boschi-Muller and Motorin 2013). The order of events for each tRNA is not fully known and the understanding of the overall process is complicated by the retrograde (cytosol to nucleus) transport of tRNAs.
In the mitochondrial matrix transcription produces long precursor RNAs, H strand transcripts and an L strand transcript, that are cleaved by mitochondrial RNase P (an entirely proteinaceous complex), ELAC2, and other nucleases to yield 12S rRNA, 16S rRNA, mRNAs, and pre-tRNAs lacking 3' CCA sequences (reviewed in Van Haute et al. 2015). TRNT1 polymerizes an untemplated CCA sequence onto the 3' ends of the pre-tRNAs and chemical modifications are made to several nucleotides in the tRNAs.
In the nucleus transcription reactions produce precursor tRNAs (pre-tRNAs) that have extra 5' leaders, 3' trailers, and, in some cases, introns which are removed by enzymes and enzyme complexes: RNase P cleaves the 5' leader, RNase Z cleaves the 3' trailer, TRNT1 polymerizes CCA onto the resulting 3' end, the TSEN complex cleaves at each end of the intron, and the tRNA ligase complex ligates the resulting exons (reviewed in Rossmanith et al. 1995, Phizicky and Hopper 2010, Suzuki et al. 2011, Abbott et al. 2014, Li and Mason 2014). The nucleotides within tRNAs undergo further chemical modifications such as methylation and deamination by a diverse set of enzymes (reviewed in Helm and Alfonzo 2014, Boschi-Muller and Motorin 2013). The order of events for each tRNA is not fully known and the understanding of the overall process is complicated by the retrograde (cytosol to nucleus) transport of tRNAs.
In the mitochondrial matrix transcription produces long precursor RNAs, H strand transcripts and an L strand transcript, that are cleaved by mitochondrial RNase P (an entirely proteinaceous complex), ELAC2, and other nucleases to yield 12S rRNA, 16S rRNA, mRNAs, and pre-tRNAs lacking 3' CCA sequences (reviewed in Van Haute et al. 2015). TRNT1 polymerizes an untemplated CCA sequence onto the 3' ends of the pre-tRNAs and chemical modifications are made to several nucleotides in the tRNAs.
This superpathway encompasses the processes by which RNA transcription products are further modified covalently and non-covalently to yield their mature forms, and the regulation of these processes. Annotated pathways include ones for capping, splicing, and 3'-cleavage and polyadenylation to yield mature mRNA molecules that are exported from the nucleus (Hocine et al. 2010). mRNA editing and nonsense-mediated decay are also annotated. Processes leading to mRNA breakdown are described: deadenylation-dependent mRNA decay, microRNA-mediated RNA cleavage, and regulation of mRNA stability by proteins that bind AU-rich elements.psnRNP assembly is also annotated here.
The aminoacylation of mature tRNAs is annotated in the "Metabolism of proteins" superpathway, as a part of "Translation".