Protein-coding gene in the species Homo sapiens
28S ribosomal protein S21, mitochondrial is a protein that in humans is encoded by the MRPS21 gene.[5][6]
Mammalian mitochondrial ribosomal proteins are encoded by nuclear genes and assist protein synthesis within the mitochondrion.[5] 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 28S subunit protein that belongs to the ribosomal protein S21P family.[6] Pseudogenes corresponding to this gene are found on chromosomes 1p, 1q, 9p, 10p, 10q, 16q, and 17q.[7] Available sequence data analyses identified splice variants that differ in the 5' UTR; both transcripts encode the same protein.[8]