The regulation of the operon metBL. The operon is repressed by metJ (Met repressor) when its bound with SAM (S-adenosylmethionine). SAM is required for metJ to bind to the promoter. Therefore, the absence of SAM activates the operon because metJ can no longer bind to the promoter. SAM is a product of the methionine pathway. The operon has two products: metB (Cystathionine gamma-synthase), metL (Bifunctional aspartokinase/homoserine dehydrogenase 2). Both of these products are enzymes used in the methionine biosynthesis. MetB catalyzes the reaction O-succinyl-L-homoserine to L,L-cystathionine. MetL catalyzes two different reactions in the methionine pathway. They include the first step (L-aspartate to 4-phospho-L-aspartate) and the third step (L-aspartate 4-semialdehyde to L-homoserine) in the creation of L-homoserine from L-aspartate.

Methionine biosynthesis; Methionine metabolism: metB, metL References