SPERMIDINE BIOSYNTHESIS IN SACCHAROMYCES-CEREVISIAE - POLYAMINE REQUIREMENT OF A NULL MUTANT OF THE SPE3 GENE (SPERMIDINE SYNTHASE)

The Saccharomyces cerevisiae SPE3 gene, coding for spermidine synthase , was cloned, sequenced, and localized on the right arm of chromosome XVI. The deduced amino acid sequence has a high similarity to mammalia n spermidine synthases, and has putative S-adenosylmethionine binding motifs. To investigate the effect of total loss of the SPE3 gene, we c onstructed a null mutant of this gene, spe3 Delta, which has no spermi dine synthase activity and has an absolute requirement for spermidine or spermine for the growth. This requirement is satisfied by a very lo w concentration of spermidine (10(-8) M) or a higher concentration of spermine (10(-6) M).