Mammalian mitochondrial ribosomes (mitoribosomes) are responsible for protein synthesis within the mitochondrion. The mitoribosomes are composed of a 4:1 ratio of protein to RNA, with the proteins forming two subunits, the 28S subunit and the 39S subunit. Across species, the proteins that make up the mitoribosome subunits vary greatly in sequence, preventing easy recognition by sequence homology. MRP-S25 (mitochondrial 28S ribosomal protein S25), also known as S25mt, is a 173 amino acid mitochondrial ribosomal protein belonging to the ribosomal protein S25/L51 family. Localized to mitochondria, MRP-S25 is present in the 28S subunit of the mitoribosomes.