Ribosomes are recycled for a new round of translation initiation by dissociation of ribosomal subunits, messenger RNA and transfer RNA from their translational post-termination complex. Here we present cryo-EM structures of the human 55S mitochondrial ribosome (mitoribosome) and the mitoribosomal large 39S subunit in complex with mitoribosome recycling factor (RRF) and a recycling-specific homolog of elongation factor G (EF-G2). These structures clarify an unusual role of a mitochondria-specific segment of RRF, identify the structural distinctions that confer functional specificity to EF-G2, and show that the deacylated tRNA remains with the dissociated 39S subunit, suggesting a distinct sequence of events in mitoribosome recycling. Furthermore, biochemical and structural analyses reveal that the molecular mechanism of antibiotic fusidic acid resistance for EF-G2 is markedly different from that of mitochondrial elongation factor EF-G1, suggesting that the two human EF-Gs have evolved diversely to negate the effect of a bacterial antibiotic.
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| http://dx.doi.org/10.1038/s41467-021-23726-4 | DOI Listing |
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