The invention relates to nucleic acids which encode fungal polypeptides with the biological activity of acetoacetyl-CoA thiolase, to the polypeptides encoded by them and to their use as targets for fungicides and to their use for identifying new, fungicidally active compounds, and to methods of finding modulators of these polypeptides and, finally, to transgenic organisms containing sequences encoding fungal polypeptides with the function of an acetoacetyl-CoA thiolase.