The ability of spermidine to stimulate antisense oligonucleotide induced ribosome frameshifting to the +1 reading frame at the UCC UGA shift site in the absence of the natural 3 0 stimulator demonstrates that this cis-acting element is not required for polyamine responsiveness. Similarly, spermidine stimulation was observed in the absence of the 5 0 element but virtually eliminated by altering the UGA codon of the shift site to UGG. These observations are in agreement with previous studies examining the importance of cis-acting elements for polyamine induced frameshifting during expression of antizyme genes (39) (40) (41) .