The recent isolation and characterization of Tri101 in Fusarium sporotrichioides has led to the functional identification of the yeast open reading frame (ORF) YLL063c, located on chromosome XII of Saccharomyces cerevisiae. The sequence of YLL063c predicts a protein of 474 residues that has 45% identity and 70% similarity to FsTri101. FsTri101 encodes a trichothecene 3-O-acetyltransferase that functions in trichothecene biosynthesis. Feeding studies indicated low levels of C3-OH acetylation in cultures of the laboratory yeast strain, RW2802. No similar activity was found in RW2802 transformed with an integrative plasmid carrying a disrupted YLL063c gene. Based on these results, which show structural and functional similarities between YLL063c and FsTri101, we propose that YLL063c encodes an acetyltransferase capable of trichothecene 3-O-acetylation and have named this gene AYT1. Published in 2002 by John Wiley & Sons, Ltd.