Characterization of the ugatA gene of Ustilago maydis, isolated by homology to the gatA gene of Aspergillus nidulans.

A gene encoding a putative GABA aminotransferase (ugatA) was isolated from the basidiomycete Ustilago maydis via heterologous hybridization to the GABA aminotransferase gene (gatA) of Aspergillus nidulans . The derived amino-acid sequence of ugatA shows strong identity throughout the protein to the GABA aminotransferase enzymes from A. nidulans and Saccharomyces cerevisiae. Northern analysis in U. maydis indicated that the ugatA transcript is inducible by the omega-amino acids GABA and beta-alanine, and is not subject to nitrogen catabolite repression. With the use of ugatA promoter-lacZ fusion constructs, it was demonstrated that the removal of sequences located approximately 250 bp 5' to the translational start site of ugatA (including multiple copies of a 7-bp direct repeat) resulted in the loss of induction by omega-amino acids. While the ugatA gene under the control of the A. nidulans gatA promoter was able to fully complement a gatA- phenotype in A. nidulans, the full-length ugatA gene was not, suggesting a lack of expression from the U. maydis promoter in A. nidulans. A U. maydis strain with a gene disruption at the ugatA locus showed decreased growth on beta-alanine as a sole nitrogen source, but was able to grow on GABA as a sole nitrogen source, indicating an alternative pathway for the utilization of GABA in U. maydis.