Mitochondrial tRNA 3' end metabolism and human disease

Abstract

Over 150 mutations in the mitochondrial genome have been shown to be associated with human disease. Remarkably, two-thirds of them are found in tRNA genes, which constitute only one-tenth of the mitochondrial genome. A total of 22 tRNAs punctuate the genome and are produced together with 11 mRNAs and 2 rRNAs from long polycistronic primary transcripts with almost no spacers. Pre-tRNAs thus require precise endonucleolytic excision. Furthermore, the CCA triplet which forms the 3' end of all tRNAs is not encoded, but must be synthesized by the CCA-adding enzyme after 3' end cleavage. Amino acid attachment to the CCA of mature tRNA is performed by aminoacyl-tRNA synthetases, which, like the preceding processing enzymes, are nuclear-encoded and imported into mitochondria. Here, we critically review the effectiveness and reliability of evidence obtained from reactions with in vitro transcripts that pathogenesis-associated mutant mitochondrial tRNAs can lead to deficiencies in tRNA 3' end metabolism (3' end cleavage, CCA addition and aminoacylation) toward an understanding of molecular mechanisms underlying human tRNA disorders. These defects probably contribute, individually and cumulatively, to the progression of human mitochondrial diseases.

Cosegregation of the G7444A mutation in the mitochondrial COI/tRNASer(UCN) genes with the 12S rRNA A1555G mutation in a Chinese family with aminoglycoside‐induced and nonsyndromic hearing loss

“…Thus, the mutated polypeptide may retain a partial function. Alternatively, the G7444A mutation is adjacent to the site of 3' end endonucleolytic processing of the L-strand RNA precursor, spanning tRNA Ser(UCN) and ND6 mRNA [Guan et al, 1998;Levinger et al, 2004]. Our previous data showed that the A7445G mutation in the precursor of tRNA Ser(UCN) led to a failure in the processing of the L-strand RNA precursor, thereby causing a marked decrease of the steady-state levels of tRNA Ser(UCN) and ND6 mRNA [Guan et al, 1998;Li et al, 2005b].…”

Genetic aspects of mitochondrial genome evolution

“…This processing, which is known as the RNA punctuation model (Ojala et al, 1980), is mediated by RNase P and tRNase Z endonucleases, respectively (Levinger et al, 2004). When multiple tRNA genes are present, as between nad3 and nad5…”

Naturally Occurring Mutations in Human Mitochondrial Pre-tRNASer(UCN) Can Affect the Transfer Ribonuclease Z Cleavage Site, Processing Kinetics, and Substrate Secondary Structure

“…Processing of mitochondrial pre-tRNA Ser(UCN) with tRNase Z S was also optimal with 2.5 mM CaCl 2 and could not be detected with Mn 2ϩ alone or in a mixture with Ca 2ϩ . In vitro pre-tRNA processing of unmodified transcripts has both advantages and limitations (4). The endonucleolytic end processing reactions may precede most of the nucleoside modifications; even so, the absence of the post-transcriptional nucleoside modifications in tRNA Ser(UCN) (e.g.…”

“…The circular 16,568-base pair human mitochondrial genome (1) is bidirectionally transcribed into long polycistronic heavy (H) 4 -and light (L)-strand precursor RNAs. Two rRNAs and 11 mRNAs encoding 13 polypeptides (all of them subunits of complexes in the respiratory transport chain) are punctuated by 22 tRNAs (1 tRNA for each of 18 amino acids and 2 each for leucine and serine with different anticodons) with very little intergenic RNA (2,3).…”

“…Eukaryotic nuclear-encoded tRNAs are transcribed from RNA polymerase III promoters with short 5Ј end leaders and 3Ј end trailers ending with a U 3 tail. The characteristic length and sequence of mitochondrial pre-tRNA leaders and trailers, on the other hand, depend on the setting of individual tRNAs among the neighboring functional RNA units (other tRNAs, mRNAs, rRNAs) on the long polycistronic H-and L-strand transcripts (4).…”