A 9.7-kilobase pair segment of the Escherichia coli chromosome spanning the hisT and purF loci has been characterized. Six genes were identified in this region by complete DNA sequence analysis, in vivo expression in maxicells, and RNA transcript analysis. S1 nuclease analysis has demonstrated that some of these genes are part of the hisT or purF operons. Two of the newly identified genes, dedA and dedB, were localized immediately downstream of hisT in the hisT operon. Two other genes, denoted dedC and dedD, have been localized between the hisT and purF operons. The other two genes, dedE and dedF flank the purF gene. dedE has been previously described as the first gene in the purF operon (Makaroff, C.A., and Zalkin, H. (1985) J. Biol. Chem. 260, 10378-10387). dedF was localized downstream from purF and is part of the purF operon. In addition, dedF is homologous to the ubiX gene of Salmonella typhimurium. Adjacent to dedF is the E. coli homologue of the S. typhimurium argT locus encoding the lysine/arginine/ornithine-binding protein. All of the genes in this region of the chromosome were found to be transcribed in a counter-clockwise direction on the E. coli map which revises the direction of purF transcription.