POLYHYDROXYNAPHTHALENE REDUCTASE INVOLVED IN MELANIN BIOSYNTHESIS IN MAGNAPORTHE-GRISEA - PURIFICATION, CDNA CLONING AND SEQUENCING

During the biosynthesis of fungal melanin, tetrahydroxynaphthalene red uctase catalyzes the NADPH-dependent reduction of 1,3,6,8-tetrahydroxy naphthalene (T4HN) into (+)-scytalone and 1,3,8-trihydroxynaphthalene into (-)-vermelone. The enzyme from Magnaporthe grisea, the fungus res ponsible for rice blast disease, has been purified to homogeneity. It is a tetramer of four identical 30-kDa subunits. A full-length cDNA cl one of about 1 kb encoding T4HN reductase has been isolated from a cDN A library constructed in the lambda ZAP II vector and characterized. T he clone contains a 846-bp open reading frame. Translation of the DNA sequence gave a 282-residue amino acid sequence with a calculated mole cular mass of 29.9 kDa. Sequences corresponding to the amino-terminal part and three internal proteolytic peptides were present in the trans lated sequence. T4HN reductase exhibits characteristics of the short-c hain alcohol dehydrogenase family. The reductase shares 56% identity w ith a putative ketoreductase involved in aflatoxin biosynthesis in Asp ergillus parasiticus.