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Abstract
Using a DNA fragment containing the Aspergillus niger abfB gene as a probe, the homologous Aspergillus nidulans gene, designated abfB, has been cloned from a genomic library containing size-selected HindIII fragments. The nucleotide sequence of the A. nidulans abfB gene shows strong homology with the A. niger abfB, Trichoderma reesei abf-1 and Trichoderma koningii α-L-arabinofuranosidase/β-xylosidase genes. Regulation of abfB expression has been investigated in cultures induced with L-arabitol. The accumulation of abfB mRNA, total α-L-arabinofuranosidase activity and AbfB protein levels have been determined in a wild-type A. nidulans strain as well as in different mutant strains. These strains are affected either in their response to ambient pH (palA1 and pacCc14 mutants), carbon catabolite repression (creAd4 mutant), the ability to utilize L-arabitol as a carbon source (araA1 mutant) or a combination of both latter genotypes (araA1 creAd4). The results obtained indicate that the expression of the A. nidulans abfB gene was higher at acidic pHs and was superinduced in this double mutant. Furthermore, disruption of the abfB gene demonstrated that in A. nidulans AbfB is the major p-nitrophenyl α-L-arabinofuranoside-hydrolysing activity but at least one minor activity is expressed, which is involved in the release of L-arabinose from polysaccharides.
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