Saccharomyces cerevisiae has a limited life span, measured by the reproductive capacity of the individual cell. Several genes that are differentially expressed during the yeast life span have been isolated. One of these genes, LAG2, has been characterized for its role in longevity. LAG2 is preferentially expressed in young cells. It encodes a predicted 680 amino acid protein with a putative transmembrane helix. The sequences does not show significant similarity to any other DNA or protein sequences in the databases. Deletion of LAG2 in a haploid strain did not affect growth, but it resulted in a 50% decrease in the mean and maximum life span. When LAG2 was overexpressed, the mean and maximum life span of the yeasts was extended by about 36% and 54%, respectively. These results indicate that this is a longevity-assurance gene in yeast.