They have an estimated 75% protein to rRNA composition compared to prokaryotic ribosomes, where this ratio is reversed.

Another difference between mammalian mitoribosomes and prokaryotic ribosomes is that the latter contain a 5S rRNA.

Among different species, the proteins comprising the mitoribosome differ greatly in sequence, and sometimes in biochemical properties, which prevents easy recognition by sequence homology.

This gene encodes a 28S subunit protein that does not seem to have a counterpart in prokaryotic and fungal-mitochondrial ribosomes.

A pseudogene corresponding to this gene is found on chromosome Xq.