The naturally occurring polyamines putrescine, spermidine or spermine are ubiquitous in all cells. Although polyamines have prominent regulatory roles in cell division and growth, precise molecular and cellular functions are not well-established in vivo. In this work we have performed microarray experiments with a spermidine synthase, spermine oxidase mutant (Deltaspe3 Deltafms1) strain to investigate the responsiveness of yeast genes to supplementation with spermidine or spermine. Expression analysis identified genes responsive to the addition of either excess spermidine (10(-5) M) or spermine (10(-5) M) compared to a control culture containing 10(-8) M spermidine. 247 genes were upregulated > two-fold and 11 genes were upregulated >10-fold after spermidine addition. Functional categorization of the genes showed induction of transport-related genes and genes involved in methionine, arginine, lysine, NAD and biotin biosynthesis. 268 genes were downregulated more than two-fold, and six genes were downregulated > eight-fold after spermidine addition. A majority of the downregulated genes are involved in nucleic acid metabolism and various stress responses. In contrast, only a few genes (18) were significantly responsive to spermine. Thus, results from global gene expression profiling demonstrate a more major role for spermidine in modulating gene expression in yeast than spermine.