-Glactosidase Activity and Lactose Utilization in Aspergillus nidulans

Abstract

SUMMARY: When mycelia of Aspergillus nidulans are grown with lactose or galactose as the carbon source, β-galactosidase activity is induced at least 30-fold. The effect of growth conditions on the formation of the activity was investigated. The enzyme has been partially characterized: two proteins with molecular weights near 120000 and 450000 have β-galactosidase activity; present evidence suggests that these are different aggregates of the same polypeptide. A mutant, lac150, is described which grows poorly on lactose and lacks β-galactosidase activity. These two characters are determined by two unlinked genes and independently expressed. This demonstrates the existence of an alternative (and unknown) mode of lactose utilization. Although β-galactosidase activity is not required for mycelial growth on lactose, it is essential for germination of conidia with lactose as the sole carbon source. Mutants unable to form β-galactosidase activity fall into three genetic groups designated bgaA, B and C. All these mutants grow normally with lactose as sole carbon source. One mutant at the bgaA locus forms a heat-labile β-galactosidase and is presumably a structural gene lesion.