The roles of assembly factors in mammalian mitoribosome biogenesis

As ancient bacterial endosymbionts of eukaryotic cells, mitochondria have retained their own circular DNA as well as protein translation system including mitochondrial ribosomes (mitoribosomes). In recent years, methodological advancements in cryoelectron microscopy and mass spectrometry have revealed the extent of the evolutionary divergence of mitoribosomes from their bacterial ancestors and their adaptation to the synthesis of 13 mitochondrial DNA encoded oxidative phosphorylation complex subunits. In addition to the structural data, the first assembly pathway maps of mitoribosomes have started to emerge and concomitantly also the assembly factors involved in this process to achieve fully translational competent particles. These transiently associated factors assist in the intricate assembly process of mitoribosomes by enhancing protein incorporation, ribosomal RNA folding and modification, and by blocking premature or non-native protein binding, for example. This review focuses on summarizing the current understanding of the known mammalian mitoribosome assembly factors and discussing their possible roles in the assembly of small or large mitoribosomal subunits.

Automated summary

Mitochondria, ancient bacterial endosymbionts of eukaryotic cells, have their own circular DNA and protein translation system. Recent advancements in cryoelectron microscopy and mass spectrometry have revealed the evolutionary divergence of mitochondrial ribosomes from their bacterial ancestors and their adaptation for synthesizing mitochondrial DNA encoded oxidative phosphorylation complex subunits. Furthermore, assembly pathway maps of mitoribosomes and associated factors have started to emerge, shedding light on the complex assembly process.