Pbytophthora Parasitica by Aminotriazole in situ and after Cloning and Expression of the Respective Gene (HIS3) in Escherichia coli

The HIS] gene of Phytophthora parasitica was isolated from a plasmid library by complementing E. coli hlS B463 to histidine prototrophy. The gene, encoding imidazoleglycero lphosphate dehydratase, was expressed in E. coli independently of the promoter of the cloning vector. The growth of Phy­ tophthora parasitica was far more sensitive to 3-amino-1,2,4-tr iazole (amitrole) than that of the E. coli W.t. The inhibition was fully counteracted by histidine. E. coli with a defective imidazoleglycero l­ phosphate dehydratase comple mented by the Phytophthora gene exhibited the same high sensitivity against amitrole as Phytophthora itself. The expression of genes in E. coli is suggested for screening potential inhibitors of enzymes in pathogenic organisms.