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

Abstract

The Magnaporthe grisea ERG2 gene, encoding delta 8-->delta 7 sterol isomerase, was isolated from a genomic library by heterologous hybridization to a fragment of the Ustilago maydis ERG2 gene. The isolated gene 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 were strongly hydrophobic, suggesting that they may function by anchoring the protein to a membrane surface. The M. grisea ERG2 gene complemented a U. maydis deletion mutant in which the ERG2 gene had been removed using a one-step gene replacement procedure. The delta 8-->delta 7 sterol isomerase produced by the M. grisea ERG2 gene exhibited a level of sensitivity to the sterol biosynthesis inhibitor, tridemorph, similar to that of the enzyme derived from the U. maydis ERG2 gene.