ISOLATION AND CHARACTERIZATION OF THE CERATO-ULMIN TOXIN GENE OF THE DUTCH ELM DISEASE PATHOGEN, OPHIOSTOMA-ULMI

The hydrophobic protein cerato-ulmin (CU), produced by Ophiostoma ulmi, has been implicated in the pathogenicity of this fungus on elm. Primers were designed based on the nucleotide sequence deduced from the published CU amino-acid sequence, and a DNA fragment of the cu gene was amplified using the polymerase chain reaction. The amplified cu fragment was used as a hybridization probe to identify and isolate the cu gene from a genomic DNA library of an aggressive isolate of O. ulmi (= O. novo-ulmi). The cu coding region is interrupted by two introns and encodes a 100 amino-acid prepro-CU polypeptide that is processed to a 75 amino-acid mature protein upon secretion. CU shows significant sequence similarity to hydrophobins secreted by certain other fungi.