The araB and araC genes of Salmonella typhimurium have been cloned onto the plasmid pBR322. Restriction analysis and subcloning of restriction fragments localized these genes to a 4.4 kb DNA fragment. Complementation analysis revealed that the cloned araB and araC genes from S. typhimurium complemented araB and araC mutant strains of escherichia coli. Conversely, cloned araB and araC genes from E. coli complemented araB and araC mutant strains of Escherichia coli. Conversely, cloned araB and araC genes from E. coli complemented araB and ara C mutant strains of S. typhimurium. The DNA sequence was determined for the S. typhimurium araB and araC controlling region and for the initially translated portions of these genes. The nucleotide sequence of the araB promoter was 87% homologous with the same region in E. coli and contained no deletions or insertions relative to the E. coli sequence. The presumed AUG codon corresponding to the amino terminus of the S. typhimurium araC protein was in the same location as in E. coli. There was, however, considerable divergence for the E. coli sequence preceding the translation start site. The nucleotide sequence of the initial 237 bp in the open reading frame of the S. typhimurium araC gene was 78% homologous with the same sequence in E. coli. By comparison, the amino acid sequence for this region was 91% conserved.