Regulation of formation of the intracellular β-gaiactosidase activity ofAspergillus nidulans

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Abstract
The regulation of formation of the single intracellular β-galactosidase activity ofAspergillus nidulans was investigated. β-Galactosidase was not formed during growth on glucose or glycerol, but was rapidly induced during growth on lactose orD-galactose.L-Arabinose, and — with lower efficacy —D-xylose also induced β-galactosidase activity. Addition of glucose to cultures growing on lactose led to a rapid decrease in β-galactosidase activity. In contrast, in cultures growing onD-galactose, addition of glucose decreased the activity of β-galactosidase only slightly. Glucose inhibited the uptake of lactose, but not ofD-galactose, and required the carbon catabolite repressor CreA for this. In addition, CreA also repressed the formation of basal levels of β-galactosidase and partially interfered with the induction of β-galactosidase byD-galactose,L-arabinose, andD-xylose.D-Galactose phosphorylation was not necessary for β-galactosidase induction, since induction byD-galactose occurred in anA. nidulans mutant defective in galactose kinase, and by the non-metabolizableD-galactose analogue fucose in the wild-type strain. Interestingly, a mutant in galactose-1-phosphate uridylyl transferase produced β-galactosidase at a low, constitutive level even on glucose and glycerol and was no longer inducible byD-galactose, whereas it was still inducible byL-arabinose. We conclude that biosynthesis of the intracellular β-galactosidase ofA. nidulans} is regulated by CreA, partially repressed by galactose-1-phosphate uridylyl transferase, and induced byD-galactose andL-arabinose in independent ways.