Identification and functional expression of tahA, a filamentous fungal gene involved in copper trafficking to the secretory pathway in Trametes versicolor.

In this study, cDNA and genomic clones encoding a homologue of the yeast gene anti-oxidant 1 (ATX1) from the white-rot fungus Trametes versicolor, a basidiomycete known to produce several laccase isoenzymes involved in lignin degradation, were identified. This gene, named Trametes ATX homologue (tahA), encodes a protein of 7.9 kDa with 56% identity to the yeast Atx1p sequence. Two different alleles of tahA were obtained that differed mainly in their intervening sequences and in a 425 nt insertion located 183 nt upstream of the transcription start site. tahA is present as one copy per haploid nucleus in T. versicolor, as shown by Southern analysis. Expression of tahA cDNA restored high-affinity iron uptake in a deltaatx1 yeast strain and oxygen sensitivity in a deltasod1 deltasod2 yeast strain, showing that tahA is also a functional homologue of ATX1. The inability of tahA to rescue the deltasod1 phenotype on copper-deficient medium indicated that tahA function is copper-dependent. Sequence analysis of the tahA promoter revealed several motifs that were similar to the conserved motifs found in the copper-regulated metallothionein and Cu, Zn superoxide dismutase genes, CUP1 and SOD1, of Saccharomyces cerevisiae, Neurospora crassa and Candida glabrata. In contrast to its yeast homologue ATX1, tahA is induced under elevated copper concentrations in the medium (>0.25 micro M CuSO(4)) and repressed under copper starvation. The transcription of tahA was analysed in response to copper and iron, and after adding xenobiotica. The results are discussed in relevance to laccase expression.