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 amine-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 construction of null mutants in both Escherichia coli and in Saccharomyces cerevisiae, and studies on the physiological effects of the resultant complete absence of spermidine and spermine. The most striking results were found with null mutants of Saccharomyces cerevisiae; these mutants have an absolute requirement for spermidine and/or spermine, and show very striking morphological changes after depletion of these amines. Depletion of spermidine and spermine in S. cerevisiae also results in a marked irreversible defect in mitochondrial structure and function.
