Pathway for the catabolism of HPA (4HPA and 3HPA) in E. coli. (A) Genetic map of the chromosomal hpa (in E. coli W) and hpc (in E. coli C) regions. Relevant genes are indicated by blocks: genes with similar shading participate in the same enzymatic step or in the same functional unit (route) of the pathway. The hpc genes are indicated in brackets. Regulatory and transport genes are shown by solid and vertically striped blocks, respectively. The genes flanking the hpa cluster (tsr, orf12, orf13, and orf14) are contiguous in the genome of E. coli K-12 and are represented by thick lines. orf12 and orf13 correspond to the yjiY gene from E. coli K-12. orf14 corresponds to the yjiA gene from E. coli K-12. The arrows show the directions of gene transcription. Bent arrows represent the Pr, Pg, Px, Pa1, Pa2 and PBC promoters. REP sequences are shown. The HpaR repressor and HpaA activator are represented by a square and hexagon, respectively; empty and solid symbols indicate inactive and active regulators, respectively; − and + indicate transcriptional repression and activation, respectively. The inducer molecule (HPA and HPC) is represented by a solid circle. (B) Biochemistry of the HPA catabolic pathway. The metabolites are 4HPA and 3HPA, HPC (homoprotocatechuate), CHMS (5-carboxymethyl-2-hydroxy-muconic semialdehyde), CHM (5-carboxymethyl-2-hydroxy-muconic acid), OPET (5-oxo-pent-3-ene-1,2,5-tricarboxylic acid), HHDD (2-hydroxy-hept-2,4-diene-1,7-dioic acid), OHED (2-oxo-hept-3-ene-1,7-dioic acid), and HHED (2,4-dihydroxy-hept-2-ene-1,7-dioic acid). The enzymes are HpaBC (HPA monooxygenase), HpaD (HPC 2,3-dioxygenase), HpaE (CHMS dehydrogenase), HpaF (CHM isomerase), HpaG (OPET decarboxylase), HpaH (hydratase), HpaI (HHED aldolase), and Sad (succinic semialdehyde dehydrogenase). The HPA transport protein (HpaX) is represented by a thick arrow. Out and In indicate outside and inside the cell, respectively.