The S.pombe protein was tested for antizyme activity using a gene fusion with glutathione S-transferase (GST). In this construct, ORF1 and ORF2 of antizyme are fused in-frame by deleting the T nucleotide that encodes U of the stop codon of ORF1. This GST±antizyme fusion gene was expressed in Escherichia coli and the protein was puri®ed by af®nity chromatography. ODC inhibitory activity was tested by incubating the recombinant antizyme protein with an S.pombe crude extract and then assaying the mixture for ODC activity. The results ( Figure 2) show that the recombinant protein can inhibit S.pombe ODC. GST alone (1 mg) does not inhibit S.pombe ODC (data not shown). In light of these results, the S.pombe gene will be called S.pombe ODC antizyme (SPA). Interestingly, the S.pombe ODC was also inhibited by mouse antizyme 1 and antizyme 2 (both expressed as GST fusions); however, the yeast fusion protein did not inhibit mouse ODC (data not shown).