A novel gene, SpTRK, has been isolated from DNA of the fission yeast Schizosaccharomyces pombe (Sp) by hybridization to an oligodeoxyribonucleotide (oligo) probe designed from a sequence fully conserved between the potassium transporter genes TRK1 and TRK2 of Saccharomyces cerevisiae (Sc). SpTRK is a single-copy gene located on Sp chromosome I. Nucleotide sequence analysis of the cloned gene identified an open reading frame (ORF) with coding capacity for a protein of 833 amino acids (aa). The predicted SpTRK aa sequence showed a high level of conservation relative to the potassium transporters of Sc and Saccharomyces uvarum (Su), particularly within their transmembrane (TM) domains and in aa required for their ion transport functions. A single SpTRK transcript of about 2.7 kb is expressed at high levels in exponentially growing Sp cells, but it is downregulated in cells from stationary cultures.