Saccharomyces cerevisiae ORF YEL070w encodes mannitol dehydrogenase (MDH), as confirmed by the present results. Six highly homologous peptide motifs were identified in the amino acid sequence of the YEL070w product by comparison with those of microbial MDH proteins. In particular, a typical coenzyme-binding site and an active site that are specific to enzymes participating in the dehydrogenation of alcohols groups were identified in these homologous peptide motifs. S. cerevisiae cells overexpressing YEL070w exhibited MDH activity showing high substrate specificity for mannitol and a coenzyme requirement of NAD(+) in the oxidation reaction. The salt-sensitive phenotype of S. cerevisiae glycerolsynthesis-deficient mutant (Delta GPD1 and Delta GPD2) was complemented and tolerance to several stressors (i.e., heat and sugar) was observed with YEL070w expression. (c) 2005 Elsevier Inc. All rights reserved.