Mammalian mitochondrial ribosomal proteins are encoded by nuclear genes and help in protein synthesis within the mitochondrion. Mitochondrial ribosomes (mitoribosomes) consist of a small 28S subunit and a large 39S subunit. 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 39S subunit protein that belongs to the EcoL15 ribosomal protein family. A pseudogene corresponding to this gene is found on chromosome 15q.Zhang Q.-H., Genome Res. 10:1546-1560(2000).Wiemann S., Genome Res. 11:422-435(2001).The MGC Project Team; Genome Res. 14:2121-2127(2004).