We have cloned and sequenced the wild-type CDC26 gene and a mutant allele, cdc26-1, of Saccharomyces cerevisiae. Nucleotide sequence analysis revealed that the gene we cloned was the same as SCD26, a dosage-dependent suppressor of cdc26. However, the cloned gene is in fact the CDC26 gene, because a nucleotide substitution in cdc26-1 was found to be a nonsense mutation in this sequence. Disruption of this gene conferred thermosensitive cell growth and the disrupted cdc26 gene could not complement the cdc26-1 mutant allele. Thus, the CDC26 gene is required for cell growth only at high temperature.