Human mitochondria require mtRF1 for translation termination at non-canonical stop codons

Area of Science:

• Mitochondrial biology
• Molecular genetics
• Protein synthesis

Background:

• Mitochondrial translation machinery differs significantly from bacterial systems.
• Human mitochondria utilize a non-universal genetic code, lacking tRNAs for AGA and AGG codons.
• The termination mechanism at these non-canonical codons (AGA/AGG) is not fully understood.

Purpose of the Study:

• To investigate the role of mitochondrial release factor 1 (mtRF1) in translation termination at AGA and AGG codons.
• To elucidate the mechanism of mitochondrial translation termination at non-canonical stop codons.

Main Methods:

• Investigated mitoribosome accumulation at AGA/AGG codons in mtRF1-deficient cells.
• Analyzed COX1 and ND6 transcript and protein levels.
• Utilized an in vitro reconstituted mitochondrial translation system to assess peptide release activity.

Main Results:

• Loss of mtRF1 led to specific mitoribosome stalling at AGA and AGG codons.
• Mitoribosome stalling affected COX1 levels but not ND6 synthesis.
• In vitro assays demonstrated mtRF1's direct peptide release activity at AGA and AGG codons.

Conclusions:

• mtRF1 plays a crucial role in mitochondrial translation termination at non-canonical AGA and AGG stop codons.
• This finding clarifies a key aspect of mitochondrial genetic code divergence and protein synthesis regulation.