title: Identification of a permease gene involved in lactose utilisation in Aspergillus nidulans.
abstract: Lactose is intracellularly hydrolysed by Aspergillus nidulans. Classical mutation mapping data and the physical characteristics of the previously purified glycosyl hydrolase facilitated identification of the clustered, divergently transcribed intracellular β-galactosidase (bgaD) and lactose permease (lacpA) genes. At the transcript level, bgaD and lacpA were coordinately expressed in response to d-galactose, lactose or l-arabinose, while no transcription was detectable in the additional presence of glucose. In contrast, creA loss-of-function mutants derepressed for both genes to a considerable extent (even) under non-inducing or repressing growth conditions. Lactose- and d-galactose induction nevertheless occurred only in the absence of glucose, indicating a regulatory role for CreA-independent repression. Remarkably, bgaD deletion mutants grew normal on lactose. In contrast, lacpA deletants grew at a much slower rate in lactose liquid medium than wild-type while strains that carried more than one copy of lacpA grew faster, showing that transport is the limiting step in lactose catabolism. The effect of lacpA gene deletion on lactose uptake was exacerbated at lower substrate concentrations, evidence for the existence of a second transport system with a lower affinity for this disaccharide in A. nidulans.
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, P.O. Box 64, H-4010 Debrecen, Hungary.
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Fekete
authors.forename: Levente
authors.initials: L
authors.lastname: Karaffa
authors.forename: Bernhard
authors.initials: B
authors.lastname: Seiboth
authors.forename: Eva
authors.initials: E
authors.lastname: Fekete
authors.forename: Christian P
authors.initials: CP
authors.lastname: Kubicek
authors.forename: Michel
authors.initials: M
authors.lastname: Flipphi
mesh_terms: D001233:Aspergillus nidulans / Q000145:classification / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D007785:Lactose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D026901:Membrane Transport Proteins; C021499:lactose permease; D001616:beta-Galactosidase; D007785:Lactose