In vitro 3 '-end endonucleolytic processing defect in a human mitochondrial tRNA(Ser(UCN)) precursor with the U7445C substitution, which causes non-syndromic deafness

Eukaryotic tRNAs are transcribed as precursors. A 5'-end leader and 3'-end trailer are endonucleolytically removed by RNase P and 3'-tRNase before 3'- end CCA addition, aminoacylation, nuclear export and translation. 3'-End-CC can be a 3'-tRNase anti-determinant with the ability to prevent mature tRN A from recycling through 3'-tRNase. Twenty-two tRNAs punctuate the two rRNA s and 13 mRNAs in long, bidirectional mitochondrial transcripts. Accurate m itochondrial gene expression thus depends on endonucleolytic excision of tR NAs. Various mitochondrial diseases and syndromes could arise from defectiv e tRNA end processing. The U7445C substitution in the human mitochondrial L -strand transcript (U74C directly following the discriminator base of tRNA( Ser(UCN))) causes non-syndromic deafness. The sequence of the precursor (G down arrow UCU) becomes G down arrow CCU, resembling a 3'-tRNase anti-deter minant. We demonstrate that a tRNA(Ser(UCN)) precursor with the U7445C subs titution cannot be processed in vitro by 3'-tRNase from human mitochondria. A 3'-end processing defect in this tRNA precursor could thus be responsibl e for mitochondrial disease.