ISOLATION AND STRUCTURAL-ANALYSIS OF THE LACCASE GENE FROM THE LIGNIN-DEGRADING FUNGUS PHLEBIA-RADIATA

We have isolated and characterized a gene coding for the laccase of the lignin-degrading fungus Phlebia radiata. The gene has nine introns and recognizable fungal promoter elements. Sequences homologous to the consensus eukaryotic heat-shock regulatory element can be found in the promoter. RNA hybridization results indicate that this gene is regulated at the transcriptional level. The derived laccase amino acid sequence shows homology to plant ascorbate oxidases, suggesting that the basic structure of the laccase is similar to the three-fold repeated beta-barrel of the ascorbate oxidases. Potential copper ligands and a residue carrying the prosthetic group pyrroloquinoline quinone (PQQ) in the laccase protein can be identified by homology. The intron/exon structure of the laccase gene suggests that this protein could have evolved by exon shuffling.