PDR4 is a gene that confers pleiotropic drug resistance (pdr) to the yeast Saccharomyces cerevisiae when present in high copy number [Leppert et al., Genetics 125 (1990) 13-20]. Transposon insertion mutations had identified the active region of the gene as a 3.7-kb SalI-EcoRI restriction fragment of the 8-kb cloned fragment. We have confirmed this by showing that this fragment is sufficient to confer pdr, and have sequenced its entire 3761 bp. It contains a single complete open reading frame (ORF) extending from nucleotide (nt) position 1631-3580, coding for a protein of 650 amino acids (aa). A 2.7-kb fragment containing this ORF is also sufficient to confer pdr. The aa sequence contains no recognizable homologies or consensus sequences, so it is a novel protein of unknown function. It is apparently soluble, since no transmembrane-type sequences were predicted. A second, partial ORF was also found, on the opposite strand, extending from nt position 774 to past the SalI site, which is apparently unrelated to pdr.