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. Prim ers were designed based on the nucleotide sequence deduced from the pu blished CU amino-acid sequence, and a DNA fragment of the cu gene was amplified using the polymerase chain reaction. The amplified cu fragme nt was used as a hybridization probe to identify and isolate the cu ge ne 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 e ncodes a 100 amino-acid prepro-CU polypeptide that is processed to a 7 5 amino-acid mature protein upon secretion. CU shows significant seque nce similarity to hydrophobins secreted by certain other fungi.