Summary auto-generated
This study reports the characterization of the Bacillus subtilis L-arabinose (ara) operon, a 11 kb chromosomal region containing nine genes. The first three genes—araA, araB, and araD—encode enzymes for L-arabinose catabolism: L-arabinose isomerase, L-ribulokinase, and L-ribulose-5-phosphate 4-epimerase, respectively. DNA sequencing revealed six additional genes—araL, araM, araN, araP, araQ, and abfA—all part of a single transcriptional unit. Sequence homology analysis indicated that araN, araP, and araQ encode components of a binding-protein-dependent transport system, while abfA likely encodes an α-L-arabinofuranosidase. The ara operon is transcribed from a single σA-like promoter located 104 nucleotides upstream of araA. Genetic analysis demonstrated that araL through abfA are not essential for L-arabinose utilization. Expression studies using lacZ transcriptional fusions revealed that the ara operon is regulated at the transcriptional level, with expression induced by L-arabinose and repressed by glucose, indicating catabolite repression mechanisms control the operon's activity.
Key findings
- The ara operon consists of nine genes in a single transcriptional unit: araA, araB, araD, araL, araM, araN, araP, araQ, and abfA, spanning approximately 11 kb of B. subtilis chromosome
- AraN, AraP, and AraQ proteins are homologous to components of binding-protein-dependent transport systems, suggesting a transport function for L-arabinose or related compounds
- The ara operon is regulated at the transcriptional level with expression induced by L-arabinose and repressed by glucose, demonstrating catabolite repression
- Genes araL through abfA are not essential for L-arabinose utilization as sole carbon source, indicating redundancy or auxillary functions
- The operon is controlled by a single σA-like promoter located upstream of araA, with all nine genes transcribed together from this promoter
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
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° 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 σA-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 α-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.