The leuLABCD operon in E. coli contains five genes that are involved in the synthesis of L-leucine. The HTH-type transcriptional regulator LeuO can activate transcription of the operon. However, if leucine tRNA is present in high amounts in the cell, indicating that levels of leucine are sufficient, it can promote early termination of the transcription after the leuL gene is transcribed. If this does not occur, transcription of the full operon will take place. The first gene in the operon, leuL, encodes the leu operon leader peptide, which may be involved in the attenuation of the transcript depending on the availability of leucine in the cell. The second gene, leuA, encodes for 2-isopropylmalate synthase, an enzyme that adds the acetyl group from acetyl-CoA to 3-methyl-2-oxobutanoate, forming 2-isopropylmalate in the first step of the biosynthesis pathway of leucine. The third gene, leuB, encodes 3-isopropylmalate dehydrogenase, an enzyme that catalyzes the oxidation of 3-isopropylmalate to 3-carboxyl-4-methyl-2-oxopentanoate in the third step of leucine biosynthesis. The fourth and fifth genes, leuC and leuD, encode for the 3-isopropylmalate dehydratase large and small subunits respectively, which combine to form the 3-isopropylmalte dehydratase protein. This is an enzyme that catalzes isomerization of 2-isopropylmalate into 3-isopropylmalate as the second step of leucine biosynthesis.

Operon: Leucine Biosynthesis References