The polyamines, putrescine, spermidine, and spermine, are major polybasic compounds in all living cells. These amines are important for many systems related to growth and differentiation. For many years we have been studying how these polyamines are synthesized, how their biosynthesis and degradation are regulated, their physiologic functions, how they act in vivo, and the structure of the various biosynthetic enzymes. For this purpose we have constructed null mutants in each of the biosynthetic steps in both Escherichia coli and in Saccharomyces cerevisiae, and have prepared overexpression systems for the biosynthetic enzymes. In our current work we have applied this background towards comparable studies on mutants of the fission yeast, S, pombe. In particular we have been interested in the effect of polyamine deprivation on cell-cycle progression.. In our recent studies with Dr. Chattopadhya. we have carried out extensive studies on the effects of polyamine deprivation on cell cycle progression in Schizosaccharomyces pombe, and on the morphological changes that occur during the development of polyamine deprivation. We have carried out these recent studies in S. pombe because this organism is particularly well suited for studies of cell cycle progression, and has elements reminiscent of animal cell division, such as contractile rings and cell division by binary fission. Abnormal patterns of growth are easily seen by microscopic observation. In addition, in this organism the effects of polyamine deficiency are seen earlier during the development of the polyamine deficiency than in S. cerevisiae. Fluorescent cell sorting studies show that, in the absence of spermidine, progression of the cell cycle stops in G1-S-phase; as little as 10-6 M spermidine is sufficient to maintain normal cell cycle distribution and normal growth.. Morphologically some of the spermidine-deprived cells become spherical at an early stage and most of them lack cell division. At later stages growth occurs in most of the cells, not by cell division but rather by cell elongation, with an abnormal distribution of materials staining with rhodamin-phalloidin (actin), DAPI, or calcofluor. More prolonged deprivation leads to profound morphological changes including nuclear degradation. In other studies we have found that amine-deficient S. pombe and E. coli mutants are markedly sensitive to the toxic effects of 95% oxygen and to hydrogen peroxide, and that they are protected from this toxicity by supplementation with polyamines.
