New insights into a fundamental process in mitochondria

New insights into a fundamental process in mitochondria
mtRF1 specifically acts on non-canonical stop codons AGA/AGG. a In vitro translation assay using mitochondrial or cytosolic ribosomes. Up to five amino-acylated tRNAs were added to the translation mixture. Elongation was assessed by measuring incorporation of radioactively labeled amino acids (*). Specificity of mitoribosomal translation was tested by the absence of mtEFG1 or by addition of fusidic acid. Means and SD of n = 3 independent experiments. Unpaired two-tailed t-test (*P < 0.05; **P < 0.01; ***P < 0.001; ns = not significant). Only relevant statistics are highlighted. b Schematic representation of the in vitro mitochondrial translation termination assay. Post-translocation complexes (POST2) containing fMQ-tRNAQ* in the P-site and either canonical stop codon UAG or non-canonical stop codons AGA/AGG in the A-site were prepared. MtRF1a/mtRF1-dependent release of dipeptide was assayed by co-sedimentation. Radioactive glutamine was used for detection. c In vitro release activity of mtRF1a and mtRF1 at UAG/AGA/AGG codons. Means and SD of n = 3 independent experiments. Unpaired two-tailed t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Credit: Nature Communications (2023). DOI: 10.1038/s41467-022-35684-6

Researchers at Karolinska Institutet have uncovered the function of the release factor mtRF1 in the final steps of mitochondrial protein synthesis. The study, published in Nature Communications, reveals new insights into a fundamental process in mitochondria.

Mitochondria are specialized organelles within the . They originate from a bacterial ancestor and maintain their own DNA molecules and gene expression machineries. Due to their importance in , they are often referred to as the "power-house of the cell."

The conversion of energy is carried out by large protein complexes located in the inner membrane of mitochondria. Central parts of these complexes are synthesized within the organelle. The synthesis pathway is unique, and many aspects of this process are still unresolved.

Combination of techniques

The researchers applied a combination of techniques, including ribosome profiling and a newly developed in vitro translation assay, to shine on the final steps of protein synthesis in mitochondria.

"The mitochondrial genetic code differs slightly from the nuclear one. We show that two uncanonical codons, which's function has been unknown, are recognized by the release factor mtRF1, signaling termination of translation," says Annika Krüger, postdoctoral researcher at the Department of Medical Biochemistry and Biophysics at Karolinska Institutet.

"This finding highlights that while in bacteria and eukaryotic cytosol have been well described for decades, we are still discovering the basic components of analogical processes in mitochondria. There is still a lot to learn," notes Joanna Rorbach, senior author of the study.

More information: Annika Krüger et al, Human mitochondria require mtRF1 for translation termination at non-canonical stop codons, Nature Communications (2023). DOI: 10.1038/s41467-022-35684-6

Journal information: Nature Communications

Citation: New insights into a fundamental process in mitochondria (2023, January 4) retrieved 20 March 2023 from
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