A search of Caenorhabditis elegans expressed sequence tag (EST) sequences with mammalian antizyme 1 sequence identi®ed 20 clones. These sequences could be deconvoluted into a contiguous cDNA sequence. Primers designed on the basis of this sequence were used to PCR amplify and subclone this cDNA from a C.elegans cDNA library. The sequence of the subcloned cDNA was con®rmed (DDBJ/EMBL/GenBank accession No. AF217278); the subsequently released genomic sequence of this C.elegans gene (DDBJ/EMBL/GenBank accession No. AF040659) con®rms our cDNA data. The amino acid sequence deduced from the cDNA sequence revealed that the longer ORF has similarity to previously reported antizyme sequences (overall 27% identity, 39% similarity to human antizyme 1; 19% identity, 34% similarity to Drosophila antizyme). These similarities are higher than that of SPA to these two antizyme genes and again are concentrated in the regions most highly conserved among previously identi®ed antizymes ( Figure 1A ). Just like mammalian antizymes, the longer ORF (ORF2) lacks an appropriate in-frame initiation codon, and expression could be provided by initiation in a short upstream overlapping ORF (ORF1) leading to +1 ribosomal frameshifting in the overlap. The putative C.elegans antizyme frameshift site (the nucleotides proximal to the end of ORF1) has 18 of 26 nucleotides identical to the consensus sequence for antizyme frameshift sites ( Figure 1B) .