Genetic organization of the HutZ and HutWXZ operon in Edwardsiella piscicida. hutW, hutX, and hutZ form the HutWXZ operon. The upstream gene of the HutWXZ operon is a 3-deoxy-7-phosphoheptulonate synthase, and the downstream gene is hemP . Similar to in other species, in E. piscicida, the corresponding operon comprises only three genes. Therefore, we named the third protein epimerase HutZ, and the operon was named HutWXZ.