FASN (Fatty Acid SyNthase; also FAS) is a cytosolic member of the short chain dehydrogenase/ reductase family 27X. It is expressed in neurons, skeletal muscle, adipocytes and hepatocytes and both catalyzes the formation of palmitic acid from acetylCoA and malonylCoA and likely mediates the transfer of fatty acids to peptides. Human FASN is 2511aa in length. It contains multiple domains, including a B-ketoacyl synthase domain (aa1-414), an acyl and malonyl transferase domain (aa429-817), an enoyl reductase domain (aa1563-1863), a B-ketoacyl reductase domain (aa1864-2118) and a thioesterase domain (aa2207-2511). FASN exists as an antiparallel homodimer. There is one theoretical alternative start site at Met2073. Over aa10-212, human FASN shares 92% aa identity with mouse FASN.