A BLAST search of the Aspergillus nidulans Database resulted, apart from a direct homologue, in two additional hits with high similarity to XlnR, a pathway-specific transcriptional activator of xylanolytic and cellulolytic system in Aspergilli. Here, we present data on one of them isolated from the contig 1.75, which is mapped on chromosome III. The coding sequence of this putative transcription factor is predicted as 2.4 kb long and is interrupted by one putative intron. Like XlnR, it contains a DNA binding domain represented by a Zn binuclear cluster found proximal to its N-terminus. Juxtaposing the physical and genetic maps of A. nidulans suggested that the predicted regulatory gene corresponds to the galA locus, which has been previously characterized to control expression of galactose kinase and galactose-1-phosphate uridyltransferase, the first two steps of D-galactose metabolism in fungi. A knockout of the aforementioned regulatory gene resulted in a lack of growth on D-galactose and galactitol indicating that the encoded transcription factor, called GalA, indeed, controls the expression of genes of both the Leloir and alternative pathways of D-galactose metabolism. GalA appeared to mediate transcription of, at least, the gal7 gene coding for galactose-1-phosphate uridyltransferase, as assessed by a Northern blot analysis. Other genes of the galactose utilization pathway were either constitutively expressed, like gal5 (encoding phosphoglucomutase) or gal10 (encoding UDP-galactose-4-epimerase), or only partially regulated, as ladA (encoding L-arabinitol-dehydrogenase required for galactitol conversion). Galactose transport apparently remained intact in the galA knockout, the result confirmed by a consumption rate of D-galactose similar to that of a wild type strain. A complete transcriptional profile of the genes related to D-galactose metabolism will be presented and a regulatory network will be discussed.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)