ISOLATION OF THE ERG2 GENE, ENCODING STEROL DELTA(8)-]DELTA(7) ISOMERASE, FROM THE RICE BLAST FUNGUS MAGNAPORTHE-GRISEA AND ITS EXPRESSION IN THE MAIZE SMUT PATHOGEN USTILAGO-MAYDIS

The Magnaporthe grisea ERG2 gene, encoding Delta(8)-->Delta(7) sterol isomerase, was isolated from a genomic library by heterologous hybridi zation to a fragment of the Ustilago maydis ERG2 gene. The isolated ge ne contained a reading frame of 745 bp which encoded a protein of 221 amino acids. The coding region was interrupted by a single putative 79 -bp-long intron. The deduced amino-acid sequence exhibited similarity to the ERG2 gene products of U. maydis and of Saccharomyces cerevisiae , particularly in the central region of the proteins. The NH2-terminal of all three proteins contained a long stretch of amino acids that we re strongly hydrophobic, suggesting that they may function by anchorin g the protein to a membrane surface. The M. grisea ERG2 gene complemen ted a U. maydis deletion mutant in which the ERG2 gene had been remove d using a one-step gene replacement procedure. The Delta(8)-->Delta(7) sterol isomerase produced by the M. grisea ERG2 gene exhibited a leve l of sensitivity to the sterol biosynthesis inhibitor, tridemorph, sim ilar to that of the enzyme derived from the U. maydis ERG2 gene.