Lactose is intracellularly hydrolysed by A. nidulans. Results from early studies enabled the in silico identification of clustered, divergently transcribed intracellular beta-galactosidase (bgaD) and putative lactose permease (lapA) genes. bglD and lapA were coexpressed in response to D-galactose, lactose or L-arabinose, while no transcription was detectable in the co-presence of glucose. By contrast, creA loss-of-function mutants featured derepression of both genes to a basal level under non-inducing conditions. However, lactose- and D-galactose induction only occurred in the absence of glucose, indicating a prominent role for CreA-independent repression in the system's regulation. To confirm lactose permease function, the lapA gene was deleted. Gene-deleted strains grew in liquid lactose media, albeit at a much lower rate than wild-type controls. On the other hand, strains that carried more than one copy of lapA progressively grew faster, showing that transport is the limiting step in lactose catabolism. The effect of lapA gene deletion on lactose uptake was exacerbated at lower concentrations, putting to evidence the existence of a second component of lower affinity for the disaccharide in A. nidulans.
Full conference title:
- Asperfest 9 (2012)