Overexpression of SPA (5±7 days derepression) leads to complete depletion of intracellular putrescine. This result implies that in S.pombe ornithine decarboxylation is the only source of putrescine synthesis (the pathway from arginine via agmatine is not utilized). The complete depletion of cadaverine in SPA overexpressing cells suggests that ODC is the only enzyme in S.pombe that can decarboxylate lysine, which is also the case in rat tissues (Pegg and McGill, 1979) .