Polyamines (putrescine, spermidine, and spermine) are major cellular components and have been shown to be involved in many systems related to growth and differentiation. Our current and older studies have been directed at learning how these polyamines are synthesized and regulated, and their physiological function. We have: (1) established the pathways for the biosynthesis of these amines in prokaryotes and eukaryotes and isolated the enzymes for the various steps in the pathways; (2) identified the genes responsible for each of the biosynthetic steps and constructed mutants with deletions in the various genes; (3) constructed plasmids that contain these genes and used the strains containing these plasmids to overproduce the encoded enzymes; (4) used the amino-deficient mutants to study the physiological effects of polyamine deprivation; (5) sequenced the gene coding for S-adenosylmethionine decarboxylase in both E. coli and S. cerevisiae and the gene coding for spermidine synthase in E. coli; (6) demonstrated that S-adenosylmethionine decarboxylase is first formed as a proenzyme in both E. coli and yeast and is cleaved post-translationally with the conversion of serine to a covalently-bound pyruvoyl group that is essential for activity; and (7) studied the effect of site-specific mutagenesis on the conversion of the proenzyme to the active enzyme. The most recent work involves the physiological effects of complete polyamine deprivation resulting from a null mutation in the gene (spe2) for S- adenosylmethionine decarboxylase in S. cerevisiae. In addition to marked microscopic changes, these polyamine-deficient cells show gross abnormalities in the cell envelope and in the mitochondria, indicating the importance of spermidine/spermine in the biosynthesis and/or integrity of these cell moieties. Many of our recent studies suggest that polyamines have a critical role in the protection of the yeast cell against oxidative damage in vivo.
