Ornithine decarboxylase (ODC) antizyme protein that negatively regulates ODC activity and intracellular polyamine biosynthesis and uptake in response to increased intracellular polyamine levels. Binds to ODC monomers, inhibiting the assembly of the functional ODC homodimer, and targets the monomers for ubiquitin-independent proteolytic destruction by the 26S proteasome. Interacts with ODC1 and thereby sterically blocks ODC homodimerization. A ribosomal frameshift occurs between the codons for Phe-42 and Asp-43. An autoregulatory mechanism enables modulation of frameshifting according to the cellular concentration of polyamines. Belongs to the ODC antizyme family.