We have used the plant toxin victorin C, which is synthesised by the saprophytic fungus Cochliobolus victoria, as a biological probe. Victorin C, labelled with either 125I or 35S, bound to eight distinct proteins (victorin-binding proteins) in oat plants that were either resistant or sensitive to the toxin. Using a series of in vitro experiments, we observed a difference in the victorin-binding properties between resistant and susceptible plants. Furthermore, we found that other plant species contain a set of proteins of similar sizes which specifically bind victorin. Unexpectedly, we also found a low molecular weight victorin-binding protein present in all tested eukaryotic and prokaryotic cells.

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