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-phosp hate 4-epimerase, respectively, have been cloned previously and the pr oducts of araB and araD were shown to be functionally homologous to th eir Escherichia coil counterparts by complementation experiments, Here we report that araA, araB and araD, whose inactivation leads to an Ar a(-) phenotype, are the first three ORFs of a nine cistron transcripti onal unit with a total length of 11 kb, This operon, called ara, is lo cated 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 iden tified within a 150 bp DNA fragment upstream from the translation star t site of araA, Analysis of the sequence of the ara operon showed that the putative products of araN, araP and araQ are homologous to bacter ial components of binding-protein-dependent transport systems and abfA most probably encodes an alpha-L-arabinofuranosidase. The functions o f araL and araM are unknown, An in vitro constructed insertion-deletio n mutation in the region downstream from araD allowed us to demonstrat e that araL, araM, araN, araP, araq and abfA are not essential for L-a rabinose utilization. Studies with strains bearing transcriptional fus ions of the operon to the E. coil lacZ gene revealed that expression f rom the ara promoter is induced by L-arabinose and repressed by glucos e.