This family of proteins corresponds to mitochondrial ribosomal subunit S27 in prokaryotes [1] and to subunit S33 in humans [2]. It is a small 106 residue protein.The evolutionary history of the mitoribosomal proteome that is encoded by a diverse subset of eukaryotic genomes, reveals an ancestral ribosome of alpha-proteobacterial descent that more than doubled its protein content in most eukaryotic lineages. Several new MRPs have originated via duplication of existing MRPs as well as by recruitment from outside of the mitoribosomal proteome [3].

1: Identification of 12 new yeast mitochondrial ribosomal proteins including 6 that have no prokaryotic homologues. Saveanu C, Fromont-Racine M, Harington A, Ricard F, Namane A, Jacquier A; J Biol Chem 2001;276:15861-15867. PMID:11278769

2: Identification of four proteins from the small subunit of the mammalian mitochondrial ribosome using a proteomics approach. Koc EC, Burkhart W, Blackburn K, Koc H, Moseley A, Spremulli LL; Protein Sci. 2001;10:471-481. PMID:11344316

3: Reconstructing the evolution of the mitochondrial ribosomal proteome. Smits P, Smeitink JA, van den Heuvel LP, Huynen MA, Ettema TJ; Nucleic Acids Res. 2007;35:4686-4703. PMID:17604309