The Bacillus Subtilis L-arabinose (ara) Operon: Nucleotide Sequence, Genetic Organization and Expression

The Bacillus subtilis L-arabinose metabolic genes araA, araB and araD, encoding L-arabinose isomerase, L-ribulokinase and L-ribulose-5-phosphate 4-epimerase, respectively, have been cloned previously and the products of araB and araD were shown to be functionally homologous to their Escherichia coli counterparts by complementation experiments. Here we report that araA, araB and araD, 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 ara, is located at about 256 degrees on the B. subtilis genetic map and contains six new genes named araL, araM, araN, araP, araQ and abfA. Expression of the ara operon is directed by a strong sigma A-like promoter identified within a 150 bp DNA fragment upstream from the translation start site of araA. Analysis of the sequence of the ara operon showed that the putative products of araN, araP and araQ are homologous to bacterial components of binding-protein-dependent transport systems and abfA most probably encodes an alpha-L-arabinofuranosidase. The functions of araL and araM are unknown. An in vitro-constructed insertion-deletion mutation in the region downstream from araD allowed us to demonstrate that araL, araM, araN, araP, araQ and abfA are not essential for L-arabinose utilization. Studies with strains bearing transcriptional fusions of the operon to the E. coli lacZ gene revealed that expression from the ara promoter is induced by L-arabinose and repressed by glucose.