CHARACTERIZATION OF 3 GENES IN THE DAM-CONTAINING OPERON OF ESCHERICHIA-COLI

The dam-containing operon in Escherichia coli is located at 74 min on the chromosomal map and contains the genes aroK, aroB, a gene called u rf74.3, dam and trpS. We have determined the nucleotide sequence betwe en the dam and trpS genes and show that it encodes two proteins with m olecular weights of 24 and 27 kDa. Furthermore, we characterize the th ree genes urf74.3, 24kDa, 27kDa and the proteins they encode. The pred icted amino acid sequences of the 24 and 27 kDa proteins are similar t o those of the CbbE and CbbZ proteins, respectively, of the Alcaligene s eutrophus cbb operon, which encodes enzymes involved in the Calvin c ycle. In separate experiments, we have shown that the 24 kDa protein h as d-ribulose-5-phosphate epimerase activity (similar to CbbE), and we call the gene rpe. Similarly, the 27 kDa protein has 2-phosphoglycola te phosphatase activity (similar to CbbZ), and we name the gene gph. T he Urf74.3 protein, with a predicted molecular weight of 46 kDa, migra ted as a 70 kDa product under denaturing conditions. Overexpression of Urf74.3 induced cell filamentation, indicating that Urf74.3 directly or indirectly interferes with cell division. We present evidence for t ranslational coupling between aroB and urf74.3 and also between rpe an d gph, Proteins encoded in the dam superoperon appear to be largely un related: Dam, and perhaps Urf74.3, are involved in cell cycle regulati on, AroK, AroB, and TrpS function in aromatic amino acid biosynthesis, whereas Rpe and Gph are involved in carbohydrate metabolism.