ISOLATION OF ASPERGILLUS-NIGER CREA MUTANTS AND EFFECTS OF THE MUTATIONS ON EXPRESSION OF ARABINASES AND L-ARABINOSE CATABOLIC ENZYMES

Aspergillus niger mutants relieved of carbon repression were isolated from an areA parental strain by selection of colonies that exhibited i mproved growth on a combination of 4-aminobutanoic acid (GABA) and D-g lucose. In addition to derepression of the utilization of GABA as a ni trogen source in the presence of a-glucose, three of the four mutants also showed derepression of L-alanine and L-proline utilization. Trans formation of the mutants with the A. niger creA gene, encoding the rep ressor protein CREA, re-established the areA phenotype on GABA/D-gluco se, identifying the mutations as creA(d). The creA gene mapped on chro mosome IV by linkage analysis and contour-clamped homogeneous electric field hybridization. The creA mutants obtained were used to study the involvement of CREA in repression by a-glucose of arabinases and L-ar abinose catabolism in A. niger. In wild-type A. niger, alpha-L-arabino furanosidase A, alpha-L-arabinofuranosidase B, endo-arabinase, L-arabi nose reductase and L-arabitol dehydrogenase were induced on L-arabinos e, but addition of a-glucose prevented this induction. Repression was relieved to varying degrees in the creA mutants, showing that biosynth esis of arabinases and L-arabinose catabolic enzymes is under control of CREA.