The L-arabinose metabolic genes and , encoding L-arabinose isomerase, L-ribulokinase and L-ribulose-5-phosphate 4-epimerase, respectively, have been cloned previously and the products of and were shown to be functionally homologous to their counterparts by complementation experiments. Here we report that and , whose inactivation leads to an Ara phenotype, are the first three ORFs of a nine cistron transcriptional unit with a total length of 11 kb. This operon, called , is located at about 256° on the genetic map and contains six new genes named and . Expression of the operon is directed by a strong σ-like promoter identified within a 150 bp DNA fragment upstream from the translation start site of . Analysis of the sequence of the operon showed that the putative products of and are homologous to bacterial components of binding-protein-dependent transport systems and most probably encodes an α-L-arabinofuranosidase. The functions of and are unknown. An -constructed insertion-deletion mutation in the region downstream from allowed us to demonstrate that and are not essential for L-arabinose utilization. Studies with strains bearing transcriptional fusions of the operon to the gene revealed that expression from the promoter is induced by L-arabinose and repressed by glucose.


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