Isolation of spermidine synthase gene (spsA) of Dictyostelium discoideum

The gene encoding spermidine synthase (spsA) was isolated from Dictyosteliu m discoideum using the technique of insertional mutagenesis. Northern blot analysis showed that the spsA mRNA is expressed maximally during the vegeta tive stage and decreases gradually during the 24 h of development. Sequenci ng of the genomic DNA and a full-length cDNA clone indicated the presence o f one intron in a gene coding for a predicted protein (SpsA) with 284 amino acids. The sequence is highly conserved, with amino acid identities compar ed to spermidine synthases of humans, 59.5%, to mouse, 61.3%, and to yeast, 58.1%. A null mutant of the spsA gene is unable to grow in the absence of exogenous spermidine. Development of spsA null cells grown in the absence o f spermidine produced fruiting bodies that have abnormally short stalks. (C ) 1999 Elsevier Science B.V. All rights reserved.