The abfB gene encoding the major alpha-L-arabinofuranosidase of Aspergillus nidulans: nucleotide sequence, regulation and construction of a disruptedstrain

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 nuc leotide sequence of the A. nidulans abfB gene shows strong homology with th e A. niger abfB, Trichoderma reesei abf-1 and Trichoderma koningii alpha-L- arabinofuranosidase/beta-xylosidase genes. Regulation of abfB expression ha s been investigated in cultures induced with L-arabitol. The accumulation o f abfB mRNA, total alpha-L-arabinofuranosidase activity and AbfB protein le vels have been determined in a wild-type A. nidulans strain as well as in d ifferent mutant strains. These strains are affected either in their respons e to ambient ph (palA1 and pacC(c)14 mutants), carbon catabolite repression (creA(d)4 mutant), the ability to utilize L-arabitol as a carbon source (a raA1 mutant) or a combination of both latter genotypes (araA1 creA(d)4). Th e results obtained indicate that the expression of the A. nidulans abfB gen e was higher at acidic pus and was superinduced in this double mutant. Furt hermore, disruption of the abfB gene demonstrated that in A. nidulans AbfB is the major p-nitrophenyl alpha-L-arabinofuranoside-hydrolysing activity b ut at least one minor activity is expressed, which is involved in the relea se of L-arabinose from polysaccharides.