MOLECULAR-BIOLOGY OF THE LIGNIN-DEGRADING BASIDIOMYCETE PHANEROCHAETE-CHRYSOSPORIUM

The white rot basidiomycete Phanerochaete chrysosporium completely deg rades lignin and a variety of aromatic pollutants during the secondary metabolic phase of growth. Two families of secreted heme enzymes, lig nin peroxidase (LiP) and manganese peroxidase (MnP), are major compone nts of the extracellular lignin degradative system of this organism. M nP and LiP both are encoded by families of genes, and the lip genes ap pear to be clustered. The lip genes contain eight or nine short intron s; the mnp genes contain six or seven short introns. The sequences sur rounding active-site residues are conserved among LiP, MnP, cytochrome c peroxidase, and plant peroxidases. The eight LiP cysteine residues align with 8 of the 10 cysteines in MnP. LiPs are synthesized as prepr oenzymes with a 21-amino-acid signal sequence followed by a 6- or 7-am ino-acid propeptide. MnPs have a 21- or 24-amino-acid signal sequence but apparently lack a propeptide. Both LiP and MnP are regulated at th e mRNA level by nitrogen, and the various isozymes may be differential ly regulated by carbon and nitrogen. MnP also is regulated at the leve l of gene transcription by Mn(II), the substrate for the enzyme, and b y heat shock. The promoter regions of mnp genes contain multiple heat shock elements as well as sequences that are identical to the consensu s metal regulatory elements found in mammalian metallothionein genes. DNA transformation systems have been developed for P. chrysosporium an d are being used for studies on gene regulation and for gene replaceme nt experiments.