title: Metabolism of D-galactose is dispensable for the induction of the beta-galactosidase (bgaD) and lactose permease (lacpA) genes in Aspergillus nidulans.
abstract: In this study, we analyze the expression of the Aspergillus nidulans bgaD-lacpA gene couple (encoding an intracellular beta-galactosidase and a lactose permease) in the presence of D-galactose. This monosaccharide can be catabolized via alternative, independent pathways in this model organism. The inductive capabilities of intermediates of the two alternative routes of D-galactose utilization were addressed in loss-of-function mutants defective in a defined step in one of the two pathways. In a galactokinase (galE9) mutant, the cluster is strongly induced by D-galactose, suggesting that formation of Leloir pathway intermediates is not required. The expression profiles of bgaD and lacpA were similar in wild type, L-arabinitol dehydrogenase (araA1), and hexokinase (hxkA1) negative backgrounds, indicating that intermediates of the oxido-reductive pathway downstream of galactitol are not necessary either. Furthermore, bgaD-lacpA transcription was not induced in any of the tested strains when galactitol was provided as the growth substrate. An hxkA1/galE9 double mutant cannot grow on d-galactose at all, but still produced bgaD and lacpA transcripts upon transfer to d-galactose. We therefore concluded that the physiological inducer of the bgaD-lacpA gene cluster upon growth on D-galactose is the nonmetabolized sugar itself.
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, Debrecen, Hungary.
authors.forename: Anita
authors.initials: A
authors.lastname: Orosz
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Fekete
authors.forename: Michel
authors.initials: M
authors.lastname: Flipphi
authors.forename: Levente
authors.initials: L
authors.lastname: Karaffa
mesh_terms: D001233:Aspergillus nidulans / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D053858:Metabolic Networks and Pathways / Q000235:genetics; D015533:Transcriptional Activation; D001616:beta-Galactosidase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D026901:Membrane Transport Proteins; C021499:lactose permease; D001616:beta-Galactosidase; D005690:Galactose
keywords: Aspergillus nidulans; Leloir pathway; beta-galactosidase; d-galactose; lactose permease; oxido-reductive pathway