Figure 4.

The role of the pSS2 in maintaining the permissive Gag to Gag‐Pol ratio. Top, in the wt gag‐pol mRNA, –1PRF on the SS1 accounts for most of the Gag‐Pol product and pSS2 is silent. Middle, a compensatory mutation in pSS2 that emerges in response to treatment with inhibitors targeting the viral protease makes pSS2 slippery. The production of Gag and Gag‐Pol is unchanged, but a small fraction of ribosomes slips into –2‐frame, resulting in synthesis of a truncated protein. Bottom, when SS1 is mutated, –1‐frameshifting on pSS2 restores Gag‐Pol production to about 70% of that on the wt sequence.