Both have (i) slippery sequences (SS) of the form X XXY YYZ (U UUU UUA for HIV-1 and G GGA AAC for PEG10), (ii) different intercodons [26 ] (GGG and UCC respectively), (iii) distinct secondary structures (SStr) (extended stem-loop for HIV-1 and pseudoknot for PEG10), and (iv) the SStr start is within the intercodon in HIV-1, whereas it is two nucleotides downstream of the intercodon in PEG10. […] The different slippery sequences, intercodons, and downstream secondary structures facilitated a frameshift efficiency that was ~2.5-fold higher for PEG10 than for HIV-1 (Fig 1 ).
Source: wiktionary