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Discrimination of initiator tRNA and start codon by mammalian mitochondrial initiation factor 3 in leaderless mRNA translation

ABSTRACT: The mammalian mitochondrial protein synthesis system produces thirteen essential subunits of oxidative phosphorylation (OXPHOS) complexes. Translation initiation in mammalian mitochondria is characterized by the use of leaderless mRNAs and non-AUG start codons, where the proofreading function of IF-3mt still remains elusive. Here, we developed a reconstituted mammalian mitochondrial translation system using in vitro transcribed and native mitochondrial tRNAs to investigate IF-3mt’s proofreading function. Similar to bacterial IF-3, IF-3mt permits initiator tRNA to participate in initiation by discriminating the three G-C pairs in its anticodon stem, and the cognate interaction of its anticodon with the AUG start codon. As a result, IF-3mt promotes the accurate initiation of leaderless mRNAs. Nevertheless, IF-3mt can also facilitate initiation from the non-AUG(AUA) start codon through its unique N- and C-terminal extensions in concert with the 5-methylcytidine (m5C) or 5-formylcytidine (f5C) modification at the anticodon wobble position of mt-tRNAMet. This is partly because the IF-3mt-specific N- and C-terminal extensions and the KKGK-motif favor leaderless mRNA initiation and relax non-AUG start codon discrimination. Analyses of IF-3mt-depleted cells revealed that, in human cells, IF-3mt indeed participates in translating the ORFs of leaderless mRNAs, as well as the internal ORFs of bicistronic mRNAs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE282838 | GEO | 2025/02/05

REPOSITORIES: GEO

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