The L-arabinose operon in Escherichia coli is a model system for the study of the control of gene expression. Maximal expression of the araBAD operon requires two positive control components: the araC protein-L-arabinose complex and the cyclic AMP receptor protein-cyclic AMP complex. Both araC protein and cyclic AMP receptor protein are required for the initiation of transcription of araBAD mRNA. We have used the plasmid pBR322 as a vector for cloning DNA fragments that contain the araBAD promoter. The cloned ara fragments were identified by both physical and genetic tests. A restriction map was constructed and the DNA sequence of the promoter was determined. The promoter contains a site that is similar to the RNA polymerase recognition sites in the galactose and lactose operons. It also contains a region similar to the known cyclic AMP receptor protein binding sites in the galactose and lactose operons.