A key regulator of cellular polyamine levels from yeasts to mammals is the protein antizyme. The antizyme gene consists of two overlapping reading frames with ORF2 in the +1 frame relative to ORFI. A programmed +1 ribosomal frameshift occurs at the last codon of ORFI and results in the production of full-length antizyme, protein. The efficiency of frameshifting is proportional to the concentration of polyamines, thus creating kin autoregulatory circuit for controlling polyamine levels. The mRNA recoding signals for frameshifting include an element 5' kind a pseudodoknot 3' of the shift site. The present work illustrates that the ORFI stop codon kind the 5' element are critical for polyamine sensing, whereas the 3' pseudoknot acts to stimulate frameshifting in a polyamine independent manner. We also demonstrate that polyamines are required to Stimulate stop codon readthrough at the MuLV redefinition site required for normal expression of the GagPol precursor protein. (c) 2005 Elsevier Inc. All rights reserved.