Thermodynamic stability and statistical significance of potential stem-loop structures situated at the frameshift sites of retroviruses.

RNA stem-loop structures situated just 3' to the frameshift sites of the retroviral gag-pol or gag-pro and pro-pol regions may make important contributions to frame-shifting in retroviruses. In this study, the thermodynamic stability and statistical significance of such secondary structural features relative to others in the sequence have been assessed using a newly developed method that combines calculations of the lowest free energy of formation of RNA secondary structures and the Monte Carlo simulations. Our results show that stem-loop structures situated just 3' to the frameshift sites are both highly stable and statistically significant relative to others in the gag-pol or gag-pro and pro-pol junction domains (both 300 nucleotides upstream and downstream from the possible frameshift sites are included) of Rous sarcoma virus (RSV), human immunodeficiency virus (HIV-1), bovine leukemia virus (BLV), human T-cell leukemia virus type II (HTLV-II), and mouse mammary tumor virus (MMTV). No other more stable, or significant folding regions are predicted in these domains.