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

Abstract tRNAs are transcribed as precursors with a 5′ end leader and a 3′ end trailer. The 5′ end leader is processed by RNase P, and in most organisms in all three kingdoms, transfer ribonuclease (tRNase) Z can endonucleolytically remove the 3′ end trailer. Long (L) and short (S) forms of the tRNase Z gene are present in the human genome. tRNase ZL processes a nuclear-encoded pre-tRNA ∼1600-fold more efficiently than tRNase ZS and is predicted to have a strong mitochondrial transport signal. tRNase ZL could, thus, process both nuclear- and mitochondrially encoded pre-tRNAs. More than 150 pathogenesis-associated mutations have been found in the mitochondrial genome, most of them in the 22 mitochondrially encoded tRNAs. All the mutations investigated in human mitochondrial tRNASer(UCN) affect processing efficiency, and some affect the cleavage site and secondary structure. These changes could affect tRNase Z processing of mutant pre-tRNAs, perhaps contributing to mitochondrial disease.