A 4906-bp DNA fragment, which complemented Schizosaccharomyces pombe strains partly defective in pyruvate dehydrogenase (PDH), was cloned and sequenced. The fragment contained an open reading frame (ORF) of 366 amino acids (aa), which showed 62% identity with the Saccharomyces cerevisiae gene encoding the PDH E1 beta subunit, and significant similarity to subunits from a number of other 2-oxo-acid dehydrogenase complexes from mammals, Gram+ and some Gram- bacteria. The clone hybridised to a 1.6-1.7-kb mRNA from wild type, and the 5' ends of the mRNA were mapped 73-83 bp upstream from the AUG start codon of the ORF. No other ORFs were found in this 4.9-kb segment of the Sz. pombe genome. Plasmids containing the ORF complemented the PDH-defective strains of Sz. pombe both for growth and for enzyme activity.