To verify that PKR was involved in the changes in HIV-1 frameshift efficiency observed with a high amount of TAR, we created two constructs, pTARibulge Ã and pTARuucg Ã , expressing mutants of TAR that cannot bind PKR (31) ( Figure 3A ). When Jurkat cells were co-transfected with pDual-HIV and plasmids generating these TAR mutants, the frameshift efficiencies were similar to that obtained in absence of TAR and significantly higher than the value obtained in the presence of wild-type TAR ( Figure 3B ). This result supports that PKR is involved in the changes of frameshift efficiency observed in the presence of TAR.