The gcvTHP operon in E. coli contains three genes that encode proteins involved in the glycine cleavage system. This system consists of four proteins, three of which are encoded in this operon, the other being the lipoamide dehydrogenase Lpd protein encoded by the lpd gene. Activation of the system occurs when large concentration of glycine are found in the cell, forming carbon dioxide, ammonia, a reduced pyridine nucleotide that cam be reused, and 5,10-methylenetetrahydrofolate. This operon can be activated by the binding of the activated cAMP-activated global transcriptional regulator CRP (CAP). CRP is activated in the presence of high levels of cAMP, which occurs typically while glucose levels are low. The operon can also be activated by the binding of activated leucine-responsive regulatory protein, (Lrp) which is activated by the binding of L-leucine. Both Lrp and CRP bind to the promoter region of the operon, activating transcription. The first gene in the operon, gcvT, encodes an aminomethyltransferase also known as the glycine cleavage system T-protein. This protein transfers the amino group from the intermediate produced by the H-protein, as well as the formation of 5,10-methylenetetrahydrofolate. The second gene, gcvH, encodes the glycine cleavage system H-protein. This protein transfers the methylamine group of glycine between the P and T-proteins of the cleavage system. The final gene in the operon, gcvP, encodes a decarboxylating glycine dehydrogenase, also known as the glycine cleavage system P-protein. This protein binds to and cleaves the amino group of glycine, transferring it to the complex with the H-protein and releasing carbon dioxide.

Operon: Glycine Cleavage System References