HIV-1 can use a cap-dependent mechanism to initiate translation of its mRNAs, like most eukaryotic mRNAs (for a review on translation initiation, see [12] [13] [14] [15] . There are two major control steps in eukaryotic cap-dependent translation initiation (see details in Figure 1A ). One is the binding of the initiator tRNA, Met-tRNA i Met , to the 40S ribosomal subunit, which requires the participation of the initiation factor 2 (eIF2) associated to GTP. The other one is the binding of the 40S subunit bearing the ternary complex to the 5 0 cap structure of the mRNA, which is controlled by the eIF4F complex. Double-stranded RNA (dsRNA), such as the TAR RNA structure, can modify the rate of translation initiation. TAR, the transactivation response element, is a 59-nt stem-bulge-loop structure present at the 5 0 and 3 0 end of all HIV-1 mRNAs in the nucleus and the cytoplasm (reviewed in 16) . It is also present under a free form of 58-66 nt in the cytoplasm of cells infected with the virus (17, 18) . In the nucleus, TAR mediates transcription activation by binding to the viral Tat protein and the cellular cyclinT protein (19, 20) . In the cytoplasm, a low concentration of TAR activates PKR, the dsRNA-dependent protein kinase, whereas a higher concentration of TAR inhibits this kinase by blocking its dimerization, which is essential for its activity (reviewed in 21) . When PKR is activated, it phosphorylates the a subunit of eIF2, interfering with translation initiation, whereas, when it is inhibited, the amount of eIF2 phosphorylated decreases and the rate of translation initiation increases.