A linear end-product pathway with gene-expression and metabolic regulation. The metabolites are denoted by x
, mRNA by mR and enzymes by E. S and P are the external metabolites. Metabolite x3 inhibits the rate of enzyme 1 through metabolic regulation and the synthesis of enzyme 1, 2 and 3 through gene-expression regulation. Enzymes 1, 2 and 3 are encoded on the same operon.