A larger family of homologous proteins includes homocitrate synthase, distinct lineages of 2-isopropylmalate synthase, several distinct, uncharacterized, orthologous sets in the Archaea, and other related enzymes. This model describes a family of 2-isopropylmalate synthases as found in yeasts and in a minority of studied bacteria. [Amino acid biosynthesis, Pyruvate family]