Mutations in ELAC2 associated with hypertrophic cardiomyopathy impair mitochondrial tRNA 3'-end processing.

Mutations in either the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial respiration. Within this group, an increasing number of mutations have been identified in nuclear genes involved in mitochondrial RNA metabolism, including ELAC2. The ELAC2 gene codes for the mitochondrial RNase Z, responsible for endonucleolytic cleavage of the 3' ends of mitochondrial pre-tRNAs.

Substitutions in conserved regions preceding and within the linker affect activity and flexibility of tRNase ZL, the long form of tRNase Z.

The enzyme tRNase Z, a member of the metallo-β-lactamase family, endonucleolytically removes 3' trailers from precursor tRNAs, preparing them for CCA addition and aminoacylation. The short form of tRNase Z, tRNase ZS, functions as a homodimer and is found in all prokaryotes and some eukaryotes. The long form, tRNase ZL, related to tRNase ZS through tandem duplication and found only in eukaryotes, possesses ~2,000-fold greater catalytic efficiency than tRNase ZS.

Tethered domains and flexible regions in tRNase Z(L), the long form of tRNase Z.

tRNase Z, a member of the metallo-β-lactamase family, endonucleolytically removes the pre-tRNA 3' trailer in a step central to tRNA maturation. The short form (tRNase Z(S)) is the only one found in bacteria and archaebacteria and is also present in some eukaryotes. The homologous long form (tRNase Z(L)), exclusively found in eukaryotes, consists of related amino- and carboxy-domains, suggesting that tRNase Z(L) arose from a tandem duplication of tRNase Z(S) followed by interdependent divergence of the domains.

Pathogenesis-related mutations in the T-loops of human mitochondrial tRNAs affect 3' end processing and tRNA structure.

Numerous mutations in the mitochondrial genome are associated with maternally transmitted diseases and syndromes that affect muscle and other high energy-demand tissues. The mitochondrial genome encodes 13 polypeptides, 2 rRNAs and 22 interspersed tRNAs via long bidirectional polycistronic primary transcripts, requiring precise excision of the tRNAs. Despite making up only ~10% of the mitochondrial genome, tRNA genes harbor most of the pathogenesis-related mutations.

Impairment of mitochondrial tRNAIle processing by a novel mutation associated with chronic progressive external ophthalmoplegia.

We report a sporadic case of chronic progressive external ophthalmoplegia associated with ragged red fibers. The patient presented with enlarged mitochondria with deranged internal architecture and crystalline inclusions. Biochemical studies showed reduced activities of complex I, III and IV in skeletal muscle.