Ornithine decarboxylase (ODC) antizyme protein that negatively regulates ODC activity and intracellular polyamine biosynthesis in response to increased intracellular polyamine levels (PubMed:15538383). Binds to ODC/SPE1 monomers, inhibiting the assembly of the functional ODC homodimer, and targets the monomers for ubiquitin-independent proteolytic destruction by the 26S proteasome (PubMed:18089576). Interacts with ODC/SPE1 and thereby sterically blocks ODC homodimerization. A ribosomal frameshift occurs between the codons for Ala-69 and Asp-70. An autoregulatory mechanism enables modulation of frameshifting according to the cellular concentration of polyamines. Belongs to the ODC antizyme family.