Distinct molecular mechanisms involved in carbon catabolite repression of the arabinose regulon in Bacillus subtilis

Abstract

The Bacillus subtilis proteins involved in the utilization of L-arabinose are encoded by the araABDLMNPQ-abfA metabolic operon and by the araE/araR divergent unit. Transcription from the ara operon, araE transport gene and araR regulatory gene is induced by L-arabinose and negatively controlled by AraR. Additionally, expression of both the ara operon and the araE gene is regulated at the transcriptional level by glucose repression. Here, by transcriptional fusion analysis in different mutant backgrounds, it is shown that CcpA most probably complexed with HPr-Ser46-P plays the major role in carbon catabolite repression of the ara regulon by glucose and glycerol. Site-directed mutagenesis and deletion analysis indicate that two catabolite responsive elements (cres) present in the ara operon (cre araA and cre araB) and one cre in the araE gene (cre araE ) are implicated in this mechanism. Furthermore, cre araA located between the promoter region of the ara operon and the araA gene, and cre araB placed 2 kb downstream within the araB gene are independently functional and both contribute to glucose repression. In Northern blot analysis, in the presence of glucose, a CcpA-dependent transcript consistent with a message stopping at cre araB was detected, suggesting that transcription 'roadblocking' of RNA polymerase elongation is the most likely mechanism operating in this system. Glucose exerts an additional repression of the ara regulon, which requires a functional araR.

Carbon Catabolite Control of the Metabolic Network inBacillus subtilis

“…The operons involved in the catabolism of secondary carbon sources are as follows (the carbon sources in parentheses): gntRKPZ (gluconate), 16,35,36) xylAB (xylose), 9) iolABCDEFGHIJ (myo-inositol), 40,41,102) trePAR (trehalose), 25,47,103) galKT (galactose), 25) glpFK (glycerol), 33) glvARC (6-P--glucoside), 34) bglPH ( -glucoside), 26,27) yjlBCD-uxaC-yjmBCD-uxuA-yjmFexuTR-uxaBA (hexuronate), 25,48) xynPB ( -xyloside), 65) yxjC-scoAE-bdh ( -hydroxybutyrate), 25,49) ara-ABDLMNPQ-abfA (arabinose) 24,52,53) and abnA xsa (arabinose), 50) kdgRKAT (hexuronate), 25,42) and kduID (galacturonate). 43) The yxkF-msmX operon probably involved in the transport of unknown sugars has been found to be under CcpA-mediated CCR.…”

Transcriptional Regulation of Genes Encoding Arabinan-Degrading Enzymes in Bacillus subtilis

“…No significant differences in the levels of glucose repression were observed during early postexponential phase (t 4 ) ( Table 3). Previously, it has been shown that glucose repression of the araABDLMNPQ-abfA metabolic operon is mainly regulated by CcpA via binding to two catabolite responsive elements (CREs), one located between the promoter region of the operon and the araA gene and one located 2 kb downstream within the araB gene (11). Mutagenesis studies of B. subtilis revealed the CRE consensus sequence TGWAARCGYTWNCW (W ϭ A or T, R ϭ A or G, Y ϭ C or T, N ϭ any base) (14,18,38,41).…”

“…The araR gene encodes the regulatory protein of L-arabinose metabolism in B. subtilis, negatively controlling the expression from the L-arabinose-inducible promoters of the ara genes (22,23). Additionally, the ara regulon is subjected to carbon catabolite repression by glucose and glycerol (11). The last gene of the L-arabinose metabolic operon, abfA, and the xsa gene located 23 kb downstream from the operon (32,40) (Fig.…”

The LacI-Type Transcriptional Regulator AraR Acts as an l -Arabinose-Responsive Repressor of l -Arabinose Utilization Genes in Corynebacterium glutamicum ATCC 31831

“…Therefore, AraR is thought to play a central role in the regulation of utilization of the multiple sugars in B. subtilis. It is noted that the L-arabinose catabolic and uptake genes are also subject to carbon catabolite repression, controlled by the cyclic AMP (cAMP)-dependent transcriptional regulator CRP in E. coli (24) and the LacI family transcriptional regulator CcpA in B. subtilis (25). These distinct regulatory systems are responsible for inhibition of L-arabinose utilization in the presence of D-glucose. Most strains of C. glutamicum tested cannot grow using L-arabinose as the sole carbon source owing to the lack of the pentose sugar utilization pathway (26).…”