The A3243G mutation in the mitochondrial gene for human mitochondrial (mt) tRNALeu(UUR), responsible for decoding of UUR codons, is associated with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). We previously demonstrated that this mutation causes defects in 5-taurinomethyluridine (τm5U) modification at the anticodon first (wobble) position of the mutant mt tRNALeu(UUR), leading to a UUG decoding deficiency and entraining severe respiratory defects. In addition, we previously identified a heteroplasmic mutation, G12300A, in the other mt leucine tRNA gene, mt tRNALeu(CUN), which functions as a suppressor of the A3243G respiratory defect in cybrid cells containing A3243G mutant mtDNA. Although the G12300A mutation converts the anticodon sequence of mt tRNALeu(CUN) from UAG to UAA, this tRNA carrying an unmodified wobble uridine still cannot decode the UUG codon. Mass spectrometric analysis of the suppressor mt tRNALeu(CUN) carrying the G12300A mutation from the phenotypically revertant cells revealed that the wobble uridine acquires de novo τm5 U modification. In vitro translation confirmed the functionality of the suppressor tRNA for decoding UUG codons. These results demonstrate that the acquisition of the wobble modification in another isoacceptor tRNA is critical for suppressing the MELAS mutation, and they highlight the primary role of the UUG decoding deficiency in the molecular pathogenesis of MELAS syndrome.
All Science Journal Classification (ASJC) codes
- Molecular Biology