Fig. 10. The molecular genetics of ornithine aminotransferase (OAT). The OAT gene is located on chromosome 10q26 and is transcribed into a 2073 base pair (bp) mRNA. Cytosolic polysomes translate the mRNA into a 439 amino acid (aa) proenzyme precursor. A mitochondrial localization signal targets the proenzyme for translocation into the mitochondria, where it is subsequently cleaved into a mature enzyme monomer. The functional OAT enzyme is believed to be a homohexamer, each monomer of which is associated with a molecule of B6.