39S ribosomal protein L22, mitochondrial is a protein that in humans is encoded by the MRPL22 gene.

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 L22 ribosomal protein family. A pseudogene corresponding to this gene is found on chromosome 4q. Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008].