Fig 1.

First step in the catabolic pathway of phenylalanine in Pseudomonas putida and organization of the genes encoding the phenylalanine hydroxylase. l-Phenylalanine is converted into l-tyrosine by the action of phenylalanine hydroxylase, made of the phhA and phhB gene products. The physical organization of the phh genes was established by Herrera and Ramos (19), and gene regulation by PhhR was as established by Herrera et al. (18). Expression of phhR is constitutive, and the ellipses represent PhhR without effector (open); once phenylalanine or tyrosine enters the cell, PhhR with the amino acid (black) is active. Crc and Crp are global regulators that influence negatively (−) or positively (+) the level of expression from the phhAB promoter. The bottom shows the physical sites to which PhhR, IHF, and Crp bind in the intergenic phhA-phhR region.