The 7472insC Mitochondrial DNA Mutation Impairs the Synthesis and Extent of Aminoacylation of tRNASer(UCN) but Not Its Structure or Rate of Turnover

Abstract

The 7472insC mitochondrial DNA mutation in the tRNA Ser(UCN) gene is associated with sensorineural deafness combined, in some patients, with a wider neurological syndrome. In cultured cybrid cells it causes a 70% decrease in tRNA Ser(UCN) abundance and mild respiratory impairment, previously suggested to be due to decreased tRNA stability. When mitochondrial transcription was blocked by ethidium bromide treatment, the half-life of the mutant tRNA was not significantly different from that of wild-type tRNA Ser(UCN) . Over-expression of mitochondrial translational elongation factor EF-Tu also had no effect on the mutant phenotype. However, during recovery from prolonged ethidium bromide treatment, the synthesis of the mutant tRNA Ser(UCN) was specifically impaired, without polarity effects on downstream tRNAs of the light strand transcription unit. We infer that the mutation acts posttranscriptionally to decrease tRNA Ser(UCN) abundance by affecting its synthesis rather than its stability. The extent of aminoacylation of the mutant tRNA was also decreased by ϳ25%. In contrast, the mutation had no detectable effect on tRNA Ser(UCN) base modification or structure other than the insertion of an extra guanosine templated by the mutation, which was structurally protected from nuclease digestion like the surrounding nucleotides. These findings indicate a common molecular process underlying sensorineural deafness caused by mitochondrial tRNA Ser(UCN) mutations.

Pathogenic mechanism of a human mitochondrial tRNA Phe mutation associated with myoclonic epilepsy with ragged red fibers syndrome

“…Diseases associated with hmt-tRNA point mutations include MERRF (myoclonic epilepsy with ragged red fibers), MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes), and deafness (2)(3)(4). Pathogenic mutations of hmt-tRNAs have been shown to affect global tRNA structure (5)(6)(7)(8), tRNA processing (9-13), modification (14)(15)(16)(17)(18)(19)(20), aminoacylation (7,(21)(22)(23)(24)(25)(26), and translation efficiency (27)(28)(29). However, little is known about the precise pathogenic mechanisms of the vast majority of hmt-tRNA mutations, hindering the development of appropriate treatments.…”

Fatal neonatal lactic acidosis caused by a novel de novo mitochondrial G7453A tRNA-Serine (UCN) mutation

“…Multiple abnormal tRNA Ser (UCN) signals in the patient's samples suggested the presence of incompletely processed forms of the tRNA. A severe structural defect of the mutant tRNA may make it primarily unstable, or prevent binding to the mitochondrial seryl-tRNA synthetase, leading to degradation of unaminoacylated tRNA (18)(19)(20). The dramatic lack of a specific tRNA explains the severe RC deficiency, leading to uncontrolled lactic acidosis and rapid progression to fatality from the disease in this infant.…”

Mitochondrial rRNA and tRNA and hearing function

“…Biochemical data showed that cell lines carrying this mutation produced a significant decrease in the level of this tRNA, which was combined with a small but clear decrease in the extent of aminoacylation. Only very subtle effects on structure or stability were found [89,90].…”